Synthesis of Carbo- and Heterocyclic Cyclopropindenes via Cycloaddition of Dienes to Cyclopropenes

Article abstract of DOI:10.1002/hlca.19940770714

The heterocyclic cyclopropindene 19 was synthesized via cycloaddition of diene 10 to the cyclopropene 11a and subsequent base-induced aromatization.While 19 is isolable, although very short-lived, the oxa analogue 18 decomposed under the conditions required for its preparation.The difluoro derivatives 14 and 15, in which the heterocyclic moiety is saturated, are accessible by the cycloaddition approach, but the corresponding dichlorides are again not isolable.Cyclopropindenes carrying substituents at C(4) have been obtained via cycloaddition of 22b to 1-bromo-2-chlorocyclopropene.The key step of the sequence is a double Curtius degradation of the cycloadduct 23b to the ketone 27a.While aromatization of the alcohol 27b provided the cyclopropindenol 28b, the reaction failed with 27a.Attempts to convert 28b to 1,3-dihydrocyclopropindene (25) via the methanesulfonate 28d failed.