Chiral Molecular Recognition by Aluminum Tris(2,6‐diphenylphenoxide) in an Asymmetric 1,4‐Addition

Ah ighly enantioselective formal conjugate allyl addition of allylboronic acids to b,g-unsaturated a-ketoesters has been realized by employing ac hiral Ni II /N,N'-dioxide complex as the catalyst. This transformation proceeds by an allylboration/oxy-Cope rearrangement sequence,p roviding af acile and rapid route to g-allyl-a-ketoesters with moderate to good yields (65-92 %) and excellent ee values (90-99 %ee). The isolation of 1,2-allylboration products provided insight into the mechanism of the subsequent oxy-Cope rearrangement reaction:s ubstrate-induced chiral transfer and ac hiral Lewis acid accelerated process.Based on the experimental investigations and DFT calculations,arare boatlike transition-state model is proposed as the origin of high chirality transfer during the oxy-Cope rearrangement.

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Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

Tang

Fang

Ruan

et al. 2019

Angewandte Chemie

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Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

et al. 2019

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Catalytic Conjugate Additions of Geminal Bis(sulfone)s: Expanding the Chemistry of Sulfones as Simple Alkyl Anion Equivalents

Landa

Puente

Santos

et al. 2009

Chemistry A European J

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The value of cyclic gem-bis(sulfone) 4 as a simple alkyl nucleophile equivalent in catalytic C-C bond-forming reactions is demonstrated. The 1,4-type nucleophilic additions of bis(sulfone) 4 to alpha,beta-unsaturated ketones take place by assistance of catalytic guanidine base. On the other hand, pyrrolidines are able to catalyze the conjugate addition of 4 to both enones and enals, likely by means of iminium ion activation. Upon exploration of the best chiral pyrrolidine catalyst, it has been found that the addition of 4 to enals catalyzed by diphenylprolinol silyl ether 10 proceeds with very high enantioselectivity (beta-aryl-substituted enals >95% ee; beta-alkyl substituted enals up to 94% ee; ee = enantiomeric excess). Further reductive desulfonation of adducts gives rise to the corresponding beta-methyl aldehydes, as well as the derived alcohols, acetals, and methyl esters after simple (Mg, MeOH) well-established protocols. Application of the procedure to the synthesis of biologically relevant phenethyl building blocks is shown. Most interestingly, alpha-alkylation of initially obtained bis(sulfone) adducts can be done even with less reactive alkylating reagents, such as long linear-chain or branched-chain alkyl halides. Accordingly, upon the desulfonation process, a general, experimentally simple and highly enantioselective access to beta-branched aldehydes, alcohols, or esters is possible. Further exploration of the method includes the use of chiral alpha,beta-unsaturated aldehydes derived from citronellal as the Michael acceptor partners. In these instances, the sense of the conjugate addition of 4 is controlled by the chirality of the pyrrolidine catalyst, thus allowing for a stereochemically predictable access to 1,3-dimethyl arrays, such as those present in deoxygenated polyketide-type natural products. The intramolecular variation of this technology by using doubly unsaturated aldehyde-ester 22 illustrated the site selectivity of the procedure and its potential for tandem processes leading to highly substituted polycyclic systems, such as 24.

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Chiral Molecular Recognition by Aluminum Tris(2,6‐diphenylphenoxide) in an Asymmetric 1,4‐Addition

Cited by 8 publications

References 34 publications

Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

Catalytic Conjugate Additions of Geminal Bis(sulfone)s: Expanding the Chemistry of Sulfones as Simple Alkyl Anion Equivalents

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