The highly syn-selective Michael reaction of enamines with 2-(1-alkenyl)-1,3-dioxolan-2-ylium cations generated from 2,2-dimethoxyethyl 2-alkenoates in situ

Article abstract of DOI:10.1016/S0040-4020(01)80900-5

2,2-Dimethoxyethyl 2-alkenoates are easily transformed into 2-(1-alkenyl)-1,3-dioxolan-2-ylium cations in situ on the action of titanium tetrachloride, which react with enamines to predominantly give syn Michael adducts in good yields. This is the first example of such a high syn-selectivity for the Michael reaction of α,β-unsaturated ester derivatives with ketone enolate equivalents.