Steric inhibition of π-electron delocalization in acyclic aryl ketones. Conformational analysis of 19-Aryl-12-methoxypodocarpa-8,11,13-trien-19-ones

Abstract

The syntheses of 12-methoxy-19-phenylpodocarpa-8,11,13-trien-19-one, 19-(p-chlorophenyl)-12- methoxypodocarpa-8,11,13-trien-19-one and 19-(p-bromophenyl)-12-methoxypodocarpa-8,11,13- trien-19-one are presented. From u.v. and ¹³C n.m.r. studies, the preferred conformation for these molecules embodies a non-coplanar arrangement of the pendant aryl ketone moiety. These compounds represent rare cases of non-coplanar acyclic aryl ketones which do not contain bulky ortho substituents.