Pyrrolidine catalyzed reactions of cyclopentadiene with alpha,beta-unsaturated carbonyl compounds.: 1,2-versus 1,4-additions

A systematic study of the reactions of cydopentadiene with alpha,beta-unsaturated carbonyl compounds in the presence of catalytic pyrrolidine-H2O revealed that the reactions can either proceed with a Michael attack at the beta-carbon of enone, or 1,2-addition to the carbonyl, leading either to 4-cyclopentadienyl-2-butanones or 6-vinylfulvenes. The former can be isolated and/or converted to the corresponding 1,2-dihydropentalenes with base (or in one-pot at longer reaction times). Substitution pattern on the enones on the competing pathways have been studied and consistent mechanisms are proposed. (C) 2015 Elsevier Ltd. All rights reserved.