EFFICIENT APPROACHES TO THE STEREOSELECTIVE SYNTHESIS OF CHIRAL 2-ALKOXYDIENES AND HETERODIENES

Three approaches to dienes having a chiral alkoxy group at C-2 are sho wn. Alkoxypropenylphosphonium salts 3 undergo stereoselective Wittig r eaction affording high yields of racemic and/or homochiral 2-menthylox y-, 2-(8-phenylmenthyloxy)-, 2-trans-phenylcyclohexyloxy- and 2-trans- mesitylcyclohexyloxybuta-1,3-dienes 5a-j (Method A). Esters derived fr om chiral alcohols 6 are methylenated with dimethyltitanocene to yield chiral dienes 5a,e,7 (Method B). Chiral alpha-alkoxyacroleins 8 are p repared by the aza-Wittig reaction of 3 followed by imine hydrolysis a nd utilized for synthesizing various types of activated chiral alkoxyc arbodienes 10,12 and 14 (Method C), as well as 3-alkoxy-1-azabutadiene derivatives 15.