SYNTHESIS OF ISOCOMENE

The total synthesis of isocomene has been accomplished in seventeen steps. Robinson annelation of 2-methylcyclopentanone with 1,4-dimethoxy-2-butanone gave 1,2,3,6,7,7a-hexahydro-4-methoxy-7a-methyl-5H-indene-5-one. Lithium aluminum hydride reduction of the latter followed by a Simmons-Smith cyclopropanation reaction with ethylidene diiodide and diethyl zinc resulted in the formation of an (alpha)-oxycyclopropylcarbinol. This was elaborated by conventional methods into the crucial intermediate, 2(alpha),4,5,7(beta)-tetramethyl-3(alpha)-methoxy-4-hydroxytricyclo{5.3.0.0('1,3)}dec-5-ene, whose cyclopropylcarbinyl rearrangement product was a cyclobutanone. Ring enlargement of the latter formed 3-oxoisocomene, from which isocomene was obtained readily