Palladium in action: domino coupling and allylic substitution reactions for the efficient construction of complex organic molecules

The palladium-catalyzed arylation and alkenylation of alkenes, generally ca lled the Heck reaction, has been applied to a number of new concepts. Start ing from simple, oligohalogenated alkenes and arenes, the synthesis of a va riety of highly functionalized carbon skeletons has been established. The d omino-type combination of an intramolecular Heck with an inter- or intramol ecular Diels-Alder reaction has been shown to provide facile access to inte resting bicyclic and tetracyclic frameworks. While intramolecular Heck reac tions on trisubstituted, cyclopropylidene-terminated alkenes proceeded with retention of the cyclopropyl moiety, tetrasubstituted alkenes with methyle necyclopropane end groups reacted with ring opening to yield cross-conjugat ed trienes. The study of the palladium-catalyzed oligocyclizations of 2-bro moalka-1,(omega-1)-diene-n-ynes has revealed interesting and useful systema tics as to achievable ring size combinations and skeletal types. Highly fun ctionalized methylenecyclopropanes are conveniently accessible via palladiu m-catalyzed allylic substitution reactions of 1-ethenylcyclopropyl sulfonat es and chlorides as well as cyclopropylideneethyl esters which proceed with complete regioselectivity in most cases. (C) 1999 Elsevier Science S,A. Al l rights reserved.