Fulvenes, fulvalenes, part 73. Synthesis of novel precursors of calicene and 7-methylcalicene

Cyclopent-2-en-1-one is a versatile electrophilic cyclopentadiene equivalen t in reactions with 1-bromo-1-lithiocyclopropanes. The synthetic sequence ( outlined in Scheme 1) has been applied to the synthesis of functionalized 7 -X-7,8-dihydrocalicenes 13c (Scheme 3) and 13d (Scheme 4). 7-Bromo-7,8-dihy drocalicene (13d) is considered to be a promising precursor of the so far u nknown parent calicene (2). A similar sequence has been realized for 7-(chl oromethyl)-7,8-dihydrocalicene (21a, Scheme 5) which, under appropriate con ditions, could give 7-methylcalicene (16).