Syntheses of New Substituted Pentacyclo(5.4.0.0(2,6).0(3,10).0(5,9))undecanes: A Novel Synthesis of Hexacyclo(6.2.1.1(3,6).0(2,7).0(4,10).0(5,9))dodecane (1,3-Bishomopentaprismane)

摘要

Several new derivatives of the pentacyclo-undecane system have been synthesized. Thus, diketone 2 could be converted to enone 3 in two ways: (i) in 69% yield via Wadsworth-Emmons reaction with the ylide derived from triethyl phosphonoacete, and (ii) in 50% overall yield via Reformatsky reaction to afford 4 followed by conversion of 4 to the corresponding mesylate and subsequent DBU-promoted elimination of methanesulfonic acid from this intermediate. Reduction of 3 with sodium borohydride-methyl hydroxide hydrogenation of 3 afforded 6 (88%). Reduction of 6 with NaBH4-MeOH afforded a mixture of lactone 7 (25%) and lactol 8 (40%); presumably 8 is formed via further reduction of 7 with excess sodium borohydride. The structure of 8 was established via dehydration to the corresponding vinyl ether, 9 (79%). Flash vacuum pyrolysis of 7 at 700 C resulted in formation of 1 (25%). This novel reaction constitutes the first example wherein pyrolysis of substituted sigma-caprolactone results in fragmentation with elimination of carbon dioxide and concomitant formation of a substituted cyclopentane.