Synthetic Applications of the Divinylcyclopropane Rearrangement and Cyclopropylphosphonium Annulating Reagents.

Abstract

Divinylcylopropane rearrangements of trans-1-carbomethoxyacetyl-2-methallylcyclopropane, 108, or its trimethylsilylenol ether 110 were used to prepare 2-carbomethoxy-4-methylcyclohept-4-en-1-one 63, a key intermediate in the synthesis of Portulal 41. Compound 63 was converted to the bicyclo{5.3.0}decene derivatives by 1-thiophenyl (38), 1-thiomethyl (119) and 1-thioisopropyl (131) cyclopropylphosphonium fluoroborates. A novel vinyl sulfide hydrolysis which is mediated by intramolecular carboxylate participation in the presence of iodine was uncovered and used as a key step in the preparation of cis-1-carbomethoxy-3-methylbicyclo{5.3.0}dec-3-en-8-one 136c, a promising intermediate which possesses functionality suitable for the further elaboration to Portulal. The divinylcyclopropane rearrangement of trans-1-methyl-1-vinyl-2-(2,6,6-trimethylcyclohex-1-enyl)cyclopropane 161 was used to form 4,7,11,11-tetramethylbicyclo{5.4.0}undeca-1,4-diene, 159, an intermediate that contains the carbon network of Widdrol and epi-Widdrol. Diene 159 was converted stereo- and regiospecifically in three steps to epi-Widdrol.