GaCl3-catalyzed Cascade Cyclization of 2-Arylcyclopropane-1,1-dicarboxylates as 1,3-Zwitterions with 3-Arylbuta-1,2-dienes

Abstract The cascade cyclization of 2-arylcyclopropane-1,1-dicarboxylates (ACDС) with 3-arylbuta-1,2-dienes in the presence of 2-2.5 equiv GaCl3 under the conditions for generation of 1,3-zwitter-ion intermediates was studied. The reaction yielded substituted 3,3a,8,8a-tetrahydrocyclopenta[a]indenes exclusively as cis,trans isomers in yields of up to 75%. This reaction was implemented both as a one-pot process and in a two-step variant with isolation of the primary cyclization products, namely, the corresponding methylidene cyclopentane-1,1-dicarboxylates. It was shown that the course of the reaction is strongly affected by the electronic effects of substituents in the aromatic moieties of ACDC and allenes.