1-amino-3-siloxy-1,3-butadienes: Highly reactive dienes for the Diels-Alder reaction

1-Amino-3-siloxy-1,3-butadienes represent a novel class of heteroatom-conta ining dienes with several useful properties. These dienes can be prepared e fficiently by deprotonation of readily available vinylogous amides with pot assium hexamethylsilazide, followed by silylation of the corresponding pota ssium enolates. This protocol has been found to be quite general for the pr eparation of various dienes containing different silyl and amino groups. Am ino siloxy dienes readily undergo [4 + 2] cycloadditions with a wide range of electron-deficient dienophiles. The reactions generally occur under very mild conditions to afford the corresponding [4 + 2] adducts in high yields and with complete regioselectivity. High endo selectivity is observed in t he case of N-phenylmaleimide and methacrolein. Other cycloadducts are usual ly obtained as mixtures of endo/exo diastereomers. The cycloadducts are ver satile synthetic intermediates. They can be subjected to deprotonation, red uction, and Wittig olefination without any hydrolysis or elimination. In ad dition, the elimination of the amino group can be cleanly accomplished unde r acidic conditions leading to the formation of enones. A variety of substi tuted cyclohexenones can be prepared by this procedure.