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Catalytic Enantioselective Construction of Quaternary Stereocenters: Assembly of Key Building Blocks for the Synthesis of Biologically Active Molecules

Liu, Yiyang and Han, Seo-Jung and Liu, Wen-Bo and Stoltz, Brian M. (2015) Catalytic Enantioselective Construction of Quaternary Stereocenters: Assembly of Key Building Blocks for the Synthesis of Biologically Active Molecules. Accounts of Chemical Research, 48 (3). pp. 740-751. ISSN 0001-4842. PMCID PMC6410712. http://resolver.caltech.edu/CaltechAUTHORS:20150302-110204535

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Abstract

The ever-present demand for drugs with better efficacy and fewer side effects continually motivates scientists to explore the vast chemical space. Traditionally, medicinal chemists have focused much attention on achiral or so-called “flat” molecules. More recently, attention has shifted toward molecules with stereogenic centers since their three-dimensional structures represent a much larger fraction of the chemical space and have a number of superior properties compared with flat aromatic compounds. Quaternary stereocenters, in particular, add greatly to the three-dimensionality and novelty of the molecule. Nevertheless, synthetic challenges in building quaternary stereocenters have largely prevented their implementation in drug discovery. The lack of effective and broadly general methods for enantioselective formation of quaternary stereocenters in simple molecular scaffolds has prompted us to investigate new chemistry and develop innovative tools and solutions. In this Account, we describe three approaches to constructing quaternary stereocenters: nucleophilic substitution of 3-halooxindoles, conjugate addition of boronic acids to cyclic enones, and allylic alkylation of enolates. In the first approach, malonic ester nucleophiles attack electrophilic 3-halooxindoles, mediated by a copper(II)-bisoxazoline catalyst. A variety of oxindoles containing a benzylic quaternary stereocenter can be accessed through this method. However, it is only applicable to the specialized 3,3-disubstituted oxindole system. To access benzylic quaternary stereocenters in a more general context, we turned our attention to the enantioselective conjugate addition of carbon nucleophiles to α,β-unsaturated carbonyl acceptors. We discovered that in the presence of catalytic palladium-pyridinooxazoline complex, arylboronic acids add smoothly to β-substituted cyclic enones to furnish ketones with a β-benzylic quaternary stereocenter in high yields and enantioselectivities. The reaction is compatible with a wide range of arylboronic acids, β-substituents, and ring sizes. Aside from benzylic quaternary stereocenters, a more challenging motif is a quaternary stereocenter not adjacent to an aromatic group. Such centers represent more general structures in chemical space but are more difficult to form by asymmetric catalysis. To address this greater challenge, and motivated by the greater reward, we entered the field of palladium-catalyzed asymmetric allylic alkylation of prochiral enolate nucleophiles about a decade ago. On the basis of Tsuji’s work, which solved the issue of positional selectivity for unsymmetrical ketones, we discovered that the phosphinooxazoline ligand effectively rendered this reaction enantioselective. Extensive investigations since then have revealed that the reaction exhibits broad scope and accepts a range of substrate classes, each with its unique advantage in synthetic applications. A diverse array of carbonyl compounds bearing α-quaternary stereocenters are obtained in excellent yields and enantioselectivities, and more possibilities have yet to be explored. As an alternative to palladium catalysis, we also studied iridium-catalyzed asymmetric allylic alkylations that generate vicinal quaternary and tertiary stereocenters in a single transformation. Overall, these methods provide access to small molecule building blocks with a single quaternary stereocenter, can be applied to various molecular scaffolds, and tolerate a wide range of functional groups. We envision that the chemistry reported in this Account will be increasingly useful in drug discovery and design.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/ar5004658DOIArticle
http://pubs.acs.org/doi/abs/10.1021/ar5004658PublisherArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6410712PubMed CentralArticle
ORCID:
AuthorORCID
Liu, Wen-Bo0000-0003-2687-557X
Stoltz, Brian M.0000-0001-9837-1528
Additional Information:© 2015 American Chemical Society. Received: December 29, 2014; Published: February 25, 2015. The authors are indebted to the efforts of many members of the Stoltz Research Group whose dedicated efforts produced the chemistry described within this Account. For financial support, we thank NIH-NIGMS (Grant R01GM080269), Amgen, the Gordon and Betty Moore Foundation, Caltech, and the Resnick Sustainability Institute at Caltech (graduate fellowship to Y.L.). S.-J.H. thanks Fulbright (Foreign Student Program, No. 15111120) and the Ilju Foundation of Education & Culture (Predoctoral Research Fellowship) for financial support. Shanghai Institute of Organic Chemistry (SIOC) is thanked for a postdoctoral fellowship to W.-B.L.
Group:Resnick Sustainability Institute
Funders:
Funding AgencyGrant Number
NIHR01GM080269-01
AmgenUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
CaltechUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Fulbright Foundation15111120
Ilju Foundation of Education & CultureUNSPECIFIED
Shanghai Institute of Organic Chemistry (SIOC)UNSPECIFIED
PubMed Central ID:PMC6410712
Record Number:CaltechAUTHORS:20150302-110204535
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150302-110204535
Official Citation:Catalytic Enantioselective Construction of Quaternary Stereocenters: Assembly of Key Building Blocks for the Synthesis of Biologically Active Molecules Yiyang Liu, Seo-Jung Han, Wen-Bo Liu, and Brian M. Stoltz Accounts of Chemical Research 2015 48 (3), 740-751 DOI: 10.1021/ar5004658
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55406
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Mar 2015 23:44
Last Modified:12 Mar 2019 15:31

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