SYNTHESIS AND PHOTOCHEMICAL-REACTION OF [4.3.2]PROPELLA-2,4,8,10-TETRAEN-7-ONE

[4.3.2]Propella-2, 4, 8, 10-tetraen-7-one (1) is synthesized from dihydroindanone in four steps in an overall yield of 10%. The electronic absorption spectrum of 1 suggests weak interactions among its it bonds, possibly longicyclic in mode. Direct photolysis of 1 leads to the formation of tricyclo[4.3.2.01, 4]undeca-2, 4, 8, 10-tetraen-7-one (18) and 6, 7-benzobicyclo[3.2.0]hepta-3, 6-dien-2-one (23) in aprotic solvents, presumably from its singlet excited state. The former product reverts to 1 upon irradiation. In methanol the interconversion between 1 and 18 is partially quenched and a labile methanol adduct, methyl 2-tricyclo[5.2.0.01, 3]nona-4, 6, 8-trieneacetate (21), is produced from both 1 and 18. The transformation of 1 into 21 proceeds stereospecifically to give endo-21 at low temperature, which equilibrates with exo-21 at room temperature, presumably via a cyclobutadiene intermediate, methyl 6-bicyclo[5.2.0]nona-l(7),2, 4, 8-tetraeneacetate (22) (15 < AG* < 22 kcal/mol). The compound 21 undergoes only polymerization possibly via 22 in solution at ambient temperature but rearranges to methyl 1-indeneacetate (25) under GLC conditions above 150 °C. © 1990, American Chemical Society. All rights reserved.