Stereoselective Synthesis of Highly Substituted Annulated Dihydropyrans Based on γ-Lithiation and Homoaldol Reaction of an Enantiopure α-Silylated Vinyl Carbamate
is converted into the corresponding [1-(trimethylsilyl)vinyl] carbamate. Its γ-lithiation by means of sec-butyllithium/TMEDA, titanation, and addition to aldehydes leads with high stereoselectivity to enantiopure anti-homoaldol products. These add, under the influence of boron trifluoride-diethyl ether complex, a second equivalent of aldehyde and form, in an intermolecular silyl-Prins reaction, the