Diastereoselective Syntheses of ( E)-α-Trialkylsilyl α,β-Unsaturated Esters, α-Silane-Substituted Conjugated Silyl Ketene Acetals, and α,γ-Substituted Allylsilanes.

Abstract

The vicinal functionalization of propiolate esters via a catalytic carbocupration/silicon group migration sequence has been further investigated to include the syntheses of a wide variety of β-alkyl- and β-aryl-substituted ( E)-α-silyl α,β-unsaturated esters. The ester substrates were transformed into their β,γ-unsaturated isomers by means of an LDA-mediated γ-deprotonation, extended silyl ketene acetal formation, and final α-protonation sequence. The silyl ketene acetal intermediates were also isolated, and their stereochemistries were established by NOE. The isolation of the intermediate extended silyl ketene acetals afforded further understanding of the lithium-extended dienolate structure and furnished additional support for Snieckus's proposed cyclic eight-membered transition state in the deprotonation of ( Z)-α,β-unsaturated carbonyls with metallodialkylamides.