Synthesis and rearrangements of the pentacyclo[5.4.0.0.0.0]undecane [1,2,4-trishomocubane] ring system

Abstract

Two syntheses of the pentacyclo[5.4.0.0^2,6.0^3,10.0^4,8]undecane (1,2,4-trishomocubane) system are described. The first synthesis involves intramolecular photochemical [2 + 2]-cycloaddition of the triquinane bisenones (14a-d) to furnish the 1,2,4-trishomocubanediones (15a-d). The second approach is based on a boron trifluoride-diethyl ether-catalysed rearrangement of the readily available Cookson's caged diketones (16a,b) to 1,2,4-trishomocubanediones (17a,b). Thermal and acid-catalysed [2 + 2]-cycloreversions of (15a,c,d) and (17a,b) to linear fused triquinanes (14a,c,d), (20a,b) and tricyclo[5.3.1.0^2,6]undecane systems of current synthetic interest are also described.