University of Groningen
Catalytic asymmetric carbon-carbon bond forming methodologies for synthesis of chiral N-containing heterocycles and chiral carboxamides
Guo, Yafei DOI:
10.33612/diss.147535855
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date: 2020
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Guo, Y. (2020). Catalytic asymmetric carbon-carbon bond forming methodologies for synthesis of chiral N-containing heterocycles and chiral carboxamides. University of Groningen.
https://doi.org/10.33612/diss.147535855
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
1
Chapter 1: Copper catalyzed alkylation of heterocyclic
acceptors with organometallics
Copper catalyzed asymmetric C-C bond forming reactions using organometallics have developed into a powerful tool for the synthesis of complex molecules with single or multiple stereogenic centers over the past decades. Among the various acceptors employed in such reactions, those with a heterocyclic core are of particular importance because of the frequent occurrence of heterocyclic scaffolds in the structures of chiral natural products and bioactive molecules. Hence, this chapter focuses on the progress made over the past 20 years for the case of heterocyclic acceptors.
Part of this chapter has been published: Y. Guo, S. R. Harutyunyan. Beilstein J. Org. Chem. 2020, 16, 1006–1021.
2
1.1 Introduction
Copper catalyzed asymmetric addition of organometallics to various acceptors is a useful strategy for C-C bond-forming reactions.1-4 These important transformations have been
thoroughly developed in the last few decades and widely used in the synthesis of chiral natural products and bioactive molecules.5-8 The majority of these molecules have a crucial
commonality, namely the presence of heterocyclic units containing nitrogen, oxygen, sulfur or other heteroatoms. These units are also often responsible for the key bioactivities that such molecules exhibit.9-11 This has motivated the development of various strategies that
target the synthesis of chiral heterocyclic motives.12-14 Among these, methodologies based
on copper catalyzed asymmetric addition of organometallics are especially valuable because of i) the compatibility between copper catalysts and the heteroatoms present in the starting materials that often show inhibitory effects in combination with other metal based catalysts, and ii) the availability and cost-efficiency of copper (I) salts and organometallics.
This chapter aims to provide an overview of the copper-based catalytic systems that enable direct application of heterocyclic acceptors in highly enantioselective C-C bond forming reactions with organometallics. The work highlighted in this chapter is divided over two sections, based on the position where the bond is formed. The first part is focused on acceptors in which the reacting unsaturated double bond is embedded into the heterocyclic ring, while the second part deals with acceptors in which the reacting unsaturated double bond is located outside of the heterocyclic unit (alkenyl-substituted heterocycles). The organometallics discussed in this chapter include organoaluminium, organozinc, organozirconium, organolithium and Grignard reagents.
1.1.1 Copper catalyzed C-C bond forming reactions at the heterocycle
Direct synthesis of chiral heterocyclic molecules from pyridine, quinoline or indole derivatives is advantageous due to the abundance of such building blocks. Unfortunately, establishing catalytic enantioselective methods for the synthesis of these compounds resulting in high yields and enantioselectivities has proven challenging. As a result, significant effort has been invested in copper catalyzed asymmetric conjugate addition reactions using organometallics (Scheme 1). In 2005, Feringa and co-workers pioneered copper catalyzed asymmetric conjugate addition (ACA) of dialkylzinc reagents to N-substituted 2,3-dehydro-4-piperidones in order to access useful chiral piperidine derivatives.15 They found the catalytic system based on chiral phosphoramidite L1 and
copper salt to be the most efficient for achieving enantioselectivities of up to 96% ee. Interestingly, piperidones with various different carbamate protecting groups (Me, Et, Ph, Tosyl and Bn) were tolerated and high enantioselectivities could also be obtained with several other dialkylzinc reagents (e.g. iPr2Zn, Bu2Zn). Later, T. Shibata and K. Endo
prepared the same product (piperidone benzyl carbamate) with a higher enantioselectivity (97% ee) by using the multinuclear phosphorus ligand catalyst L2.16 Organoaluminium
reagents are also commonly used organometallics in copper catalyzed ACA reactions. For example, in the work of Feringa et al.15 the methylation reaction using Me2Zn resulted in a
low 44% yield due to the difficult purification of the crude product. However, the same authors showed later that copper catalyzed ACA of Me3Al to Boc-protected 4-piperidone
can be used as a key step in the total synthesis of natural product (+)-Myrtine.17 For this
application the highest yield (73%) and enantioselectivity (96% ee) was obtained using a combination of chiral ligand L3 and a copper salt as catalyst.
3 Scheme 1: Copper catalyzed ACA of organometallics to piperidones and application to the total synthesis of
(+)-Myrtine.
Despite the fact that examples of high yields and enantioselectivities have been reported for conjugate additions of both organoaluminium and organozinc reagents, these reagents also present major drawbacks, namely their commercial availability and atom efficiency, given that only one alkyl group is transfered from the organometallic to the Michael acceptor. In contrast, Grignard reagents are very favourable organometallics in terms of both their availability and atom efficiency. On the other hand, Grignard reagents are significantly more reactive than organoaluminium and organozinc reagents, rendering catalytic control of both the regio- and enantio-selectivity in addition reactions challenging. Nevertheless, the Harutyunyan group introduced in 2019 the first general catalytic methodology to access a wide variety of chiral piperidones while using Grignard reagents (Scheme 1).18 In this case,
a new catalytic system based on ligand L4/Cu complex promoted the addition of Grignard reagents to N-Cbz-pyridone and N-Cbz-2,3-dihydropyridone Michael acceptors with high enantioselectivities and yields. It is worth mentioning that in copper catalyzed additions of Grignard reagents to N-Cbz-pyridone the use of Lewis acid (BF3·OEt2) together with the
4
enantioselectivities (up to 99% ee).
Although organoaluminium, organozinc, and Grignard reagents were all successfully applied in the ACA of 2,3-dehydro-4-piperidones, introduction of the vinyl group was not successful until 2012, when Alexakis and co-workers disclosed that vinyl alanes could be used in the copper catalyzed ACA to N-substituted-2,3-dehydro-4-piperidones (Scheme 2).19
Scheme 2: Copper catalyzed ACA of alkenyl alanes to N-substituted-2,3-dehydro-4-piperidones.
Optimization studies revealed that the combination of ligand L5 and Cu(II) naphthenate complex constitute the most efficient catalytic system, allowing the synthesis of the corresponding products with good yield and enantiomeric purity (up to 83% yield and 97% ee). Furthermore, a large variety of vinyl alanes was investigated and one of the final products was further derivatized into an important building block.
In 2009, Feringa and co-workers presented the first highly enantioselective 1,2-addition of dialkylzinc reagents to N-acyl-4-MeO-pyridinium salt using a copper/phosphoramidite catalytic system (Scheme 3).20
5
salts formed in situ.
The authors highlighted that the N-acyl-pyridinium salts are unstable species and that their instability affects the regioselectivity of the dearomatization process upon nucleophilic addition of organizinc reagents. To solve this problem the intermediate of N-acyl-4-MeO-pyridinium salt must be formed in situ and added slowly to the solution of Cu(OTf)2/L6
complex and dialkylzinc reagents at -78 oC. Several dialkylzinc reagents were found to be
effective as nucleophile in this reaction, in most cases providing products with high enantioselectivities and moderate yields. An exception was found with ipropyl zinc, for which only 56% ee could be obtained. The methodology has also been successfully applied to the total synthesis of the natural alkaloid (R)-Coniine.
Organozirconium is another class of organometallics that has been used widely in the synthesis of complex molecules. Recently, Fletcher and co-workers demonstrated the applicability of hydrozirconation in the ACA reaction to cyclic conjugate substrates,21-25
while the S ebesta group was the first to report the copper catalyzed addition of organozirconium reagents to N-substituted-2-3-dehydro-4-piperidones (Scheme 4).26
Scheme 4: Copper catalyzed ACA of organozirconium reagents to N-substituted-2-3-dehydro-4-piperidones
and lactams.
In the latter work, the organozirconium reagents were generated first in situ by hydrozirconation of alkenes. Subsequently, the L1/Cu catalytic system was used to test different organozirconium reagents. The results showed that for N-substituted-2,3-dehydro-4-piperidones several substrates can be obtained with moderate enantioselectivities (up to 92:8 er), but with yields limited to 22%.
The oxygen containing heterocyclic compounds are ubiquitous in natural products and medicines, with many of them chiral. Copper catalyzed ACA reactions of organometallics have also been employed to synthesize such chiral oxygen-containing heterocyclic
6
compounds. Feringa’s group presented the highly regio- and enantioselective copper catalyzed direct conjugate addition of Grignard reagents to chromones and coumarins (Scheme 5).27-28 A variety of Grignard reagents, including linear, secondary alkyl
magnesium reagents and various chromones and coumarins were tolerated by the catalytic system, providing products with high yields and enantioselectivities. It was also demonstrated that the products can be used for further transformations. Taking the enolate intermediate derived from the addition of EtMgBr to coumarin as an example, it was shown that upon treatment with an amine this enolate produces the final chiral amide product with good yield (82%) and ee (96%).
Scheme 5: Copper catalyzed ACA of Grignard reagents to chromones and coumarins.
While the methodology for ACA of Grignard reagents to chromones and coumarins has been established successfully, quinolones remained challenging substrates for such transformations until very recently. It was not until 2019 that this problem was solved, when the Harutyunyan group employed a catalytic system based on L4/Cu, which efficiently catalyzes the ACA of Grignard reagents to N-protected quinolones at room temperature (Scheme 6).18 Initially, the methodology was developed for additions to
N-Cbz-4-quinolone based substrates, and the catalytic system was demonstrated to facilitate the addition of a wide variety of reagents, including linear, α-, β-, and γ-substituted, as well as aryl Grignard reagents. Subsequent broadening of the quinolone scope revealed that substrates bearing Me, Br, CF3, ether, amide, or ester substituents are also tolerated
successfully. When the methodology was applied to the ACA of Grignard reagents to N-substituted-2-quinolones, their reactivity transpired to be an issue. Performing the reaction
7
in the presence of TMSBr resolved this problem, however, and allowed the reaction to proceed between a variety of Grignard reagents and substrates with excellent enantioselectivities. Finally, the catalytic system was applied to the synthesis of the natural product (+)-Angustureine with excellent outcome (92% yield, 97% ee).
8
Copper catalyzed ACA of organometallics has also been applied to lactams, which are useful building blocks for synthetic chemistry. In 2004, Feringa and co-workers successfully introduced the methodology of copper catalyzed ACA of organoaluminium and organozinc reagents to lactams (Scheme 7).29 They found that with a phenyl carbamate protecting
group on the nitrogen atom the addition of Et2Zn and Me3Al can be promoted by the L1/Cu
catalytic system, leading to the corresponding alkylated products with 95% and 68% enantioselectivities, respectively. Later, Harutyunyan’s group showed that also non-activated lactams with alkyl protected groups can undergo ACA reaction with EtMgBr with 93% ee (Scheme 7).30 The group of Alexakis was able to push this chemistry further and
developed a methodology that allows access to chiral lactams with quaternary stereocenters using CuTc/L5- catalyzed ACA of Et3Al to β-substituted conjugated lactams
(Scheme 7).31
Scheme 7: Copper catalyzed ACA of organometallics to lactams.
Chiral lactones form yet another interesting class of heterocyclic substrates that have attracted a lot of attention for their usefulness in both organic and medicinal chemistry. Copper catalyzed ACA of organozinc reagents to 5,6-dihydro-2H-pyran-2-one is one of the best methods to obtain chiral lactones. During the past two decades, the groups of Chan, Hoveyda, Mauduit and Wang presented a variety of methods employing chiral ligands
(L9-L13) that, in combination with copper, efficiently catalyzed the ACA of Et2Zn to
5,6-dihydro-2H-pyran-2-one (Scheme 8), providing access to chiral -substituted lactone with enantioselectivities and yields of up to 99%.32-36
9 Scheme 8: The ligands of copper catalyzed ACA of Et2Zn to 5,6-dihydro-2H-pyran-2-one.
Although the copper catalyzed ACA of Et2Zn to 5,6-dihydro-2H-pyran-2-one has been
reported, the reactivity and commercial availability of the former renders the ACA of Grignard reagents a more attractive methodology. Feringa and co-workers were the first to report copper catalyzed ACA of alkyl Grignard reagents to pyranones and 5,6-dihydro-2H-pyran-2-one (Scheme 9).37 In the presence of the Cu/L7 catalytic system several alkyl
Grignard reagents can undergo ACA to form the chiral lactones with high enantioselectivities. Importantly, the authors showed how the conjugate addition products can be further derivatised to lead to versatile chiral building blocks such as β-alkyl substituted aldehydes (66% yield, 94:6 er) or β-bromo-γ-alkyl substituted alcohol (71% yield, 93:7 er).
10
Scheme 10: Copper catalyzed AAA of organozirconium to heterocyclic acceptors.
Asymmetric allylic alkylation (AAA) is a very useful method that allows enantioselective formation of C-C bonds and copper catalyzed AAA using Grignard, organolithium, organoaluminium, and zirconium reagents has been reported. In 2015, Fletcher and co-workers presented copper-catalyzed AAA of racemic 3,6-dihydro-2H-pyrans using alkylzirconocenes in the presence of the Cu/L14 catalytic system (Scheme 10).38 Several
alkylzirconocenes were examined, resulting in the respective products with 45-93% ee and 20-33% yields. The same group has also described copper catalyzed desymmetrization of heterocyclic meso-compounds via the AAA reaction, once again using alkylzirconocenes as nucleophiles (Scheme 10). In this reaction, two seven members heterocyclic bisphosphates (O and N) undergo Cu/L15-catalyzed AAA and provide the corresponding chiral products with good yields and high enantioselectivities (92-93% ee).39
Ring opening reactions, where carbon-carbon bonds are formed upon addition of organometallics to heterocyclic acceptors, resulting in products that are not heterocyclic, provide an alternative strategy to generate important building blocks with two stereocenters, starting from heterocyclic substrates. Copper catalyzed ring opening of oxygen-bridged heterocyclic acceptors with trialkylaluminium reagents was explored by the group of Alexakis in 2009 (Scheme 11).40 Various chiral phosphoramidite ligands, in
combination with copper salt, were found to be efficient catalysts for this transformation, with the best results obtained with ligand L16.
11 Scheme 11: Copper catalyzed ring opening of oxygen-bridged substrate with trialkylaluminium reagents. Feringa and co-workers elaborated the copper catalyzed ring opening reaction of oxabicyclic alkene substrates using organolithium reagents, finding excellent anti selectivities and enantioselectivities (Scheme 12).41 During the optimization studies, they
discovered that when the Lewis acid BF3·OEt2 is employed in combination with the Cu/L1
catalyst system, the anti diastereoisomer can be obtained with 97% enantioselectivity. In addition, this methodology tolerates nBuLi, iBuLi, nHexLi and EtLi, providing full conversion and high anti selectivity and enantioselectivity in all cases.
Scheme 12: Copper catalyzed ring opening of oxabicyclic substrate with organolithium reagents.
Alexakis and co-workers exploited the copper catalyzed asymmetric ring opening of polycyclic meso-hydrazines with organoaluminium reagents (Scheme 13).42 This reaction
occurs in a classical allylic substitution pathway. Interestingly, the organoaluminium reagents in this reaction do not only act as alkyl donor, but can also activate the leaving group. After testing several kinds of phosphoramidite-type ligands with copper salts, the catalyst system L17/CuTc was selected for further studies. The solvent was found to play a crucial role in this reaction, with MTBE the solvent of choice. Various organoaluminium reagents and protecting groups were examined, providing products with good yields (up to 90%) and enantiomeric excesses (up to 95%).
12
Scheme 13: Copper catalyzed ring opening of meso-hydrazine.
1.1.2 Copper catalyzed conjugate addition reactions of organometallics to alkenyl-substituted heterocycles
Chiral heterocyclic aromatic compounds are crucial motifs in natural products and bioactive molecules and in recent years, many strategies have been reported for their highly enantioselective synthesis. However, while catalytic asymmetric C-C bond formation by ACA of organometallics is a routine procedure for additions to common Michael acceptors such as enones, enals or enoates, examples of catalytic asymmetric additions to alkenyl-N-heteroaromatic compounds are less developed. This deficiency is largely due to the intrinsically low reactivity of alkenyl-substituted heterocycles towards nucleophilic addition compared to common Michael acceptors. A way to lift this barrier was introduced in 2016 by Harutyunyan and co-workers, who developed a general methodology for direct and facile access to a variety of chiral heterocyclic aromatic compounds by ACA of Grignard reagents to conjugated alkenyl-N-heteroaromatic compounds (Scheme 14).43 The key of the
presented solution is the enhancement of the reactivity of the alkenyl-heteroaromatic substrates via Lewis acid activation in combination with readily available and highly reactive Grignard reagents and a copper catalyst bound to a chiral diphosphine ligand. Using this methodology various chiral heteroaromatic products were obtained with high enantioselectivities (up to 99% ee) and yields (up to 95%). Remarkably, both alkyl and aromatic Grignard reagents provide high yields and enantioselectivities in this methodology. Furthermore, the same group reported in a follow up study one-pot conjugate addition to alkenyl-heteroarenes with subsequent trapping of the resulting aza-enolate with reactive Michael acceptors.44
13 Scheme 14: Copper catalyzed ACA of Grignard reagents to alkenyl-substituted aromatic N-heterocycles. While pyridines are among the most important classes of heterocyclic moieties that occur in many bioactive molecules, such as natural products, pharmaceuticals, and agrochemicals, the initial report by Harutyunyan et al. did not include alkenyl-pyridines in their substrate scope.The reason for this was the markedly lower reactivity of alkenyl-pyridines towards nucleophilic addition as compared to other alkenyl-heteroarenes.
Scheme 15: Copper catalyzed ACA of Grignard reagents to β-substituted alkenyl-pyridines.
For the same reason the synthesis of chiral pyridine derivatives has always been considered a challenge in organic chemistry research. In an attempt to overcome this reactivity issue
14
the same authors decided to use trimethylsilyl based Lewis acid (TMSOTf) in order to allow covalent activation of the alkenyl-pyridine via pyridinium formation. This strategy turned out successful and optimization studies identified reaction conditions that allow highly enantioselective ACA of Grignard reagents to alkenyl-pyridines (Scheme 15).45 Using the
optimised conditions (Cu/L7/TMSOTf) a large variety of pyridine based chiral compounds were synthesized. Apart from allowing the introduction of different linear, branched, cyclic, and functionalised alkyl chains at the β-position of alkenyl-pyridines, the catalytic system also shows high functional group tolerance, thus allowing straightforward chemical transformations of the addition products.
Scheme 16: Copper catalyzed ACA of organozinc reagents to alkylidene Meldrum’s acids.
Meldrum’s acid and its derivatives are versatile reagents in organic synthesis that can be transformed into a wide range of compounds. In 2006, the group of Fillion described highly enantioselective synthesis of all-carbon benzylic quaternary stereocenters via conjugate addition of dialkylzinc reagents to alkylidene Meldrum’s acids, resulting in ACA products with high enantiopurity (scheme 16).46-51 Different kinds of Meldrum’s acid derivatives can
be tolerated in this reaction and the products can undergo various chemical transformations. Later on, this methodology was also demonstrated to enable 1,6-addition of dialkylzinc reagents to functionalized alkylidene Meldrum’s acids, providing the resulting products with moderate (65%) yields and enantioselectivities (70% ee).
1.2 Outline of this thesis
Many excellent methodologies have been reported to date to access N-containing chiral molecules and the key to the success of these transformations lies in the capability of chiral copper catalysts to activate both the nucleophile and heterocyclic acceptors towards the reaction. The development of various chiral ligands has allowed a rather broad scope of heterocycles to undergo reactions with organometallics. However, the current state of the field is certain to be incomplete and future developments in both substrate and organometallics scope are to be expected. Therefore the major aim of these thesis was to
15
expand the toolbox for accessing valuable N-containing chiral molecules using efficient and sustainable methodologies.
Hence, chapter 2 describes the Cu-catalyzed enantioselective conjugate addition of Grignard reagents to N-heterocyclic acceptors to access a wide variety of chiral 2- and 4-substituted tetrahydro-quinolones, dihydro-4-pyridones and piperidones, molecules of significant importance in medicinal chemistry.
Chapter 3 describes the first general catalytic methodology to directly access chiral dihydro-4-pyridones with excellent yields and enantioselectivities via dearomatization of activated N-acylpyridinium salts in situ, employing alkyl organomagnesium reagents as nucleophiles.
Chapter 4 presents the first Cu-catalyzed direct asymmetric conjugate addition of alkyl Grignard reagents to conjugated dienyl amides and policonjugated diamides with excellent chemo-, regio- and enantioselectivities.
Finally, chapter 5 demonstrates that in the presence of Lewis acids, it is possible to use Lewis acid/base interactions to control/override the reactivity of the dominant functional group thus allowing selective reactions with less reactive functional group in the presence of the more reactive one without a use of protecting groups thus providing new strategy for protecting group free transformations.
1.3 References
[1] S. R. Harutyunyan, T. den Hartog, K. Geurts, A. J. Minnaard, B. L. Feringa. Chem. Rev.
2008, 108, 2824-2852.
[2] A. Alexakis, J. E. Backvall, N. Krause, O. Pa mies, M. Die guez. Chem. Rev. 2008, 108, 2796-2823.
[3] T. Jerphagnon, M. G. Pizzuti, A. J. Minnaard, B. L. Feringa. Chem. Soc. Rev. 2009, 38, 1039-1075.
[4] T. E. Schmid, S. Drissi-Amraoui, C. Cre visy, O. Basle , M. Mauduit. Beilstein J. Org. Chem.
2015, 11, 2418-2434.
[5] R. W. Bates, S. Sridhar. J. Org. Chem. 2008, 73, 8104-8105.
[6] M. K. Brown, A. H. Hoveyda. J. Am. Chem. Soc. 2008, 130, 12904-12906. [7] Y. J. Chin, S. Y. Wang, T. P. Loh. Org. Lett. 2009, 11, 3674-3676.
[8] C. L. Pereira, Y. H. Chen, F. E. McDonald. J. Am. Chem. Soc. 2009, 131, 6066-6067. [9] R. Rani, C. Granchi. Eur. J. Med. Chem. 2015, 97, 505-524.
[10] M. G. Vinogradov, O. V. Turova, S. G. Zlotin. Org. Biomol. Chem. 2019, 17, 3670-3708. [11] V. Sharma, P. Kumar, D. Pathak. J. Heterocycl. Chem. 2010, 47, 491-502.
[12] Y. K. Chung, G. C. Fu. Angew. Chem. Int. Ed. 2009, 48, 2225-2227.
[13] S. Fustero, J. Moscardo, D. Jimenez, M. D. Pe rez‐Carrio n, M. Sa nchez‐Rosello , C. del Pozo. Chem. Eur. J. 2008, 14, 9868-9872.
[14] K. Takahashi, M. Midori, K. Kawano, J. Ishihara, S. Hatakeyama. Angew. Chem. Int. Ed.
2009, 47, 6244-6246.
[15] R. S ebesta, M. G. Pizzuti, A. J. Boersma, A. J. Minnaard, B. L. Feringa. Chem. Commun.
2005, 13, 1711-1713.
[16] K. Endo, M. Ogawa, T. Shibata. Angew. Chem. Int. Ed. 2010, 49, 2410-2413.
[17] M. G. Pizzuti, A. J. Minnaard, B. L. Feringa. Org. Biomol. Chem. 2008, 6, 3464-3466. [18] Y. Guo, S. R. Harutyunyan. Angew. Chem. Int. Ed. 2019, 58, 12950-12954.
16
[19] D. Müller, A. Alexakis. Org. Lett. 2012, 14, 1842-1845.
[20] M. A . Ferna ndez‐Iba n ez, B. Macia. M. G. Pizzuti, A. J. Minnaard, B. L. Feringa. Angew. Chem. Int. Ed. 2009, 48, 9339-9341.
[21] E. Rideau, H. You, M. Sidera, T. D. Claridge, S. P. Fletcher. J. Am. Chem. Soc. 2017, 139, 5614-5624.
[22] Z. Gao, S. P. Fletcher. Chem. Sci. 2017, 8, 641-646.
[23] P. Schäfer, M. Sidera, T. Palacin, S. P. Fletcher. Chem. Commun. 2017, 53, 12499-12511. [24] R. Ardkhean, P. M. Roth, R. M. Maksymowicz, A. Curran, Q. Peng, R. S. Paton, S. P. Fletcher. ACS Catal. 2017, 7, 6729-6737.
[25] J. Y. J. Wang, T. Palacin, S. P. Fletcher. Org. Lett. 2018, 21, 378-381.
[26] I. Ne methova , S. Bilka, R. S ebesta. J. Organomet. Chem. 2018, 856, 100-108.
[27] C. Vila, V. Hornillos, M. Fan ana s-Mastral, B. L. Feringa. Chem. Commun. 2013, 49, 5933-5935.
[28] J. F. Teichert, B. L. Feringa. Chem. Commun. 2011, 47, 2679-2681.
[29] M. Pineschi, F. Del Moro, F. Gini, A. J. Minnaard, B. L. Feringa. Chem. Commun. 2004, 10, 1244-1245.
[30] M. Rodrí guez-Ferna ndez, X. Yan, J. F. Collados, P. B. White, S. R. Harutyunyan. J. Am. Chem. Soc. 2017, 139, 14224-14231.
[31] P. Cottet, D. Müller, A. Alexakis. Org. Lett. 2013, 15, 828-831.
[32] L. Liang, L. Su, X. Li, A. S. Chan. Tetrahedron Lett. 2003, 44, 7217-7220.
[33] M. Tian, Z. B. Pang, H. F. Li, L. L. Wang. Tetrahedron: Asymmetry. 2017, 28, 330-337. [34] M. Yan, Z. Y. Zhou, A. S. Chan. Chem. Commun. 2000, 2, 115-116.
[35] M. K. Brown, S. J. Degrado, A. H. Hoveyda. Angew. Chem. Int. Ed. 2005, 44, 5306-5310. [36] H. Clavier, L. Coutable, L. Toupet, J. C. Guillemin, M. Mauduit. J. Organomet. Chem.
2005, 690, 5237-5254.
[37] B. Mao, M. Fan ana s-Mastral, B. L. Feringa. Org. Lett. 2013, 15, 286-289. [38] E. Rideau, S. P. Fletcher. Beilstein J. Org. Chem. 2015, 11, 2435-2443. [39] R. Jacques, R. D. Pullin, S. P. Fletcher. Nat. Commun. 2019, 10, 21.
[40] C. Ladjel, N. Fuchs, J. Zhao, G. Bernardinelli, A. Alexakis. Eur. J. Org. Chem. 2009, 29, 4949-4955.
[41] P. H. Bos, A. Rudolph, M. Perez, M. Fan ana s-Mastral, S. R. Harutyunyan, B. L. Feringa. Chem. Commun. 2012, 48, 1748-1750.
[42] L. Palais, C. Bournaud, L. Micouin, A. Alexakis. Chem. Eur. J. 2010, 16, 2567-2573. [43] R. P. Jumde, F. Lanza, M. J. Veenstra, S. R. Harutyunyan. Science. 2016, 352, 433-437. [44] F. Lanza, J. M. Pe rez, R. P. Jumde, S. R. Harutyunyan. Synthesis. 2019, 51, 1253-1262. [45] R. P. Jumde, F. Lanza, T. Pellegrini, S. R. Harutyunyan. Nat. commun. 2017, 8, 2058. [46] E. Fillion, A. Wilsily. J. Am. Chem. Soc. 2006, 128, 2774-2775.
[47] A. M. Dumas, E. Fillion. Acc. Chem. Soc. 2010, 43, 440-454. [48] A. Wilsily, E. Fillion. J. Org. Chem. 2009, 74, 8583-8594. [49] A. Wilsily, E. Fillion. Org. Lett. 2008, 10, 2801-2804.
[50] E. Fillion, A. Wilsily, E. T. Liao. Tetrahedron: Asymmetry. 2006, 17, 2957-2959. [51] A. Wilsily, T. Lou, E. Fillion. Synthesis. 2009, 2066-2072.
