122. P. Müller, Z. Miao,
     “Synthesis of Carbo- and Heterocyclic Cycloprop[f]indenes via cycloaddition of dienes to cyclopropenes”
     Helv. Chim. Acta 1994, 77, 1826-1836.

The heterocyclic cycloprop[f]indene 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. Cycloprop[f]indenes 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 cycloprop[f]indenol 28b, the reaction failed with 27a. Attempts to convert 28b to 1,3-dihydrocycloprop[f]indene (25) via the methanesulfonate 28d failed.

DOI : 10.1002/hlca.19940770714 

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