Synthesis of cycloproparenes via aromatization of 7‐Oxanorbornenes with Low‐Valent titanium

Abstract 1H‐Cyclopropa[b]naphthalene 3c and the 2,7‐diphenyl‐substituted derivative 3a have been synthesized via cycloaddition of the appropriate isobenzofurans 1a and 1b to 1‐bromo‐2‐chlorocyclopropene and aromatization of the adducts with low‐valent Ti. The same procedure afforded the 2,7‐dimethyl‐H‐cyelopropa[g]isoquinoline (15), but failed for the parent azacompound. Reaction of adducts of furans to 1‐bromo‐2‐chlorocyclopropenes with low‐valent Ti produced mixtures of cyclopropabenzenes 19 and 1,6‐dihalogeno‐1,3,5‐cycloheptatrienes 18. The latter could be converted to cyclopropabenzenes with BuLi.