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 called the Heck reaction, has been applied to a number of new concepts. Starting from simple, oligohalogenated alkenes and arenes, the synthesis of a variety of highly functionalized carbon skeletons has been established. The domino-type combination of an intramolecular Heck with an inter- or intramolecular Diels-Alder reaction has been shown to provide facile access to interesting bicyclic and tetracyclic frameworks. While intramolecular Heck reactions on trisubstituted, cyclopropylidene-terminated alkenes proceeded with retention of the cyclopropyl moiety, tetrasubstituted alkenes with methylenecyclopropane end groups reacted with ring opening to yield cross-conjugated trienes. The study of the palladium-catalyzed oligocyclizations of 2-bromoalka-1,(omega-1)-diene-n-ynes has revealed interesting and useful systematics as to achievable ring size combinations and skeletal types. Highly functionalized methylenecyclopropanes are conveniently accessible via palladium-catalyzed allylic substitution reactions of 1-ethenylcyclopropyl sulfonates and chlorides as well as cyclopropylideneethyl esters which proceed with complete regioselectivity in most cases. (C) 1999 Elsevier Science S,A. All rights reserved.