Diastereocontrol in open-chain nucleophilic attack on a double bond adjacent to a stereogenic centre carrying a silyl group

Abstract

The bis[dimethyl(phenyl)silyl]cuprate reagent introduces a silyl group to the beta-position of three alpha,beta-unsaturated esters: methyl Z-4-dimethyl(phenyl)silylpent-2-enoate 11, and methyl Z- and E-(1'-dimethylphenylsilylbenzyl)but-2-enoates 14 and 15, diastereoselectively in the unexpected sense, syn to the silyl group in the conformation in which the hydrogen atom is 'inside'. The selectivity is low (58:42) in the first case 11, where the nucleophilic attack is adjacent to the stereogenic centre carrying the silyl group, and moderate (72:28) for both Z- and E-alpha,beta-unsaturated esters 14 and 15, where the nucleophilic attack is at the other end of the double bond from the stereogenic centre. It is conceivable that nucleophilic attack actually takes place in a conformation in which the donor substituent, the silicon-carbon bond, is out of conjugation with the double bond.

New Reactions Exploring the Chemical Spaces of the Aldol Addition of Active Methylene Compounds

“…Nevertheless a simple alkylation reaction of the 1.3:1 mixture of diastereomers Furthermore the possibility to obtain known molecules in a more convenient way was highlighted by the synthesis of known valuable diols 5 (R 1 = Ph, R 2 = R 3 = Me and R 1 = Ph, R 2 = Me, R 3 = t-Bu), useful intermediates in the synthesis of substituted b-lactams and b-lactones 6. 16 These compounds were easily obtained in high yield and in a shorter sequence (reduction and deprotection reactions) 15d than those reported in the literature and without the use of toxic metal reagents. 16 The developed MCRs of Scheme 1 are not enantioselective.…”

“…16 These compounds were easily obtained in high yield and in a shorter sequence (reduction and deprotection reactions) 15d than those reported in the literature and without the use of toxic metal reagents. 16 The developed MCRs of Scheme 1 are not enantioselective. Considering the spaces of chemical reactions, how could the development of asymmetric versions of these methodologies be possible?…”

Electrophilic Fluorodesilylation of Allenylmethylsilanes: A Novel Entry to 2-Fluoro-1,3-dienes

“…Silicon-containing π-nucleophiles are extremely valuable synthetic intermediates, reacting with electrophiles in an S E 2‘ fashion to give structurally diverse products . In these reactions, the silyl group enhances the reactivity of the π-nucleophile and controls the sense of regiocontrol upon addition of the electrophile.…”