SYNTHESIS AND CHEMISTRY OF SUBSTITUTED BENZOCYCLOPROPENES

[摘要] 1H-Cyclopropa b phenanthrene (33) was synthesized in 89% yield by dehydrohalogenation of la-bromo-9a-chlorola,2,9,9a-tetrahydro-1H-cyclopropa b phenanthrene 43 with potassium t-butoxide in THF at -20(DEGREES)C. A key step in the synthesis of 33 was the Diels-Alder reaction of 1-bromo-2-chlorocyclopropene 38 with 1,2-dimethylene-1,2,-3,5,6,7,8,9-octahydronaphthalene (41). The compound did not exhibit any unusual spectral properties. 1,2-Dihydrocyclobuta b phenanthrene 49 was also synthesized via the cycloaddition of 41 with dimethyl cyclobutene-1,2-dicarboxylate. Cycloproparenes incorporating a second ring fusion were prepared via the Diels-Alder reaction of 38 with various dienes, followed by dehydrohalogenation of the Diels-Alder adducts with potassium t-butoxide. This method permitted the synthesis of the symmetrically annelated 3,4,5-trihydro-1H-cycloprop f indene 67 and 3,4,5,6-tetrahydro-1H-cyclopropa b naphthalene 69, as well as the asymmetrically annelated compounds 4,5,6-trihydro-1H-cycloprop e indene 71 and 4,5,6,7-tetrahydro-1H-cyclopropa a naphthalene 73. The nonlinearly fused cycloproparenes 71 and 73 were treated with several electrophiles to determine the degree of regioselectivity of cleavage of the three-membered ring. Compound 71, containing the five-membered second ring annelation, was highly regioselective with most electrophiles, giving either the alpha- or beta- substituted indans. Compound 73, containing the six-membered second ring fusion, gave a mixture of alpha- and beta-substituted tetralins with all reagents. The high regioselectivity of 64 has been attributed to rehybridization of the orbitals due to the additional strain imposed by the second ring fusion.

[发布机构] Rice University