Novel and selective #alpha#-substitution of ketones and other carbonyl compounds based on Pd-catalyzed cross coupling of #alpha#,#beta#-unsaturated carbonyl derivatives containing #alpha#-halogen or #alpha#-metal groups

摘要

The Pd-catalyzed cross coupling of either #alpha#-haloenones with organometals or #alpha#-metalloenones with organic halides in intrinsically more problematical than the corresponding reaction of #beta#-substituted enones or ordinary alkenyl derivatives. Nonetheless, satisfactory procedures have been developed for cross coupling with organometals containing Zn, Sn, B and Cu to give #alpha#-organylenones in high yields. As in the other cases, organozincs generally display the highest reactivity. In highly demanding and/or delicate situations, some indirect protocols involving protection of carbonyl groups or their temporary reduction help overcome difficulties encountered in direct #alpha#-substitution. Conjugate reduction and conjugate addition of #alpha#-substituted enones provide the corresponding saturated carbonyl compounds in completely regiocontrolled manner. Together with the ability to accommodate unsaturated organic groups, such as aryl, alkenyl, and alkynyl, the new Pd-catalyzed #alpha#-substitution protocols developed since 1987 promise to become synthetic tools of widespread application.