Synthesis and photoreaction of tricyclo[5.2.2.02,6]undecanes in the excited singlet (1S) state: a novel and stereospecific route to protoilludanoids

Abstract

A novel and general approach to the synthesis of functionalised protoilludane skeletons having fusedfour-, six- and five-membered rings is described. A photochemical sigmatropic 1,3-acyl shift in endo-tricyclo[5.2.2.0^2,6]undecanes having a β,γ-unsaturated carbonyl chromophore, and π^4s + π^2s cycloaddition of spiro[cyclohexa-2,4-diene-oxiran]-6-one are the key features of this approach. An efficient one-step synthesis of the epoxy ketone 11 by π^4s + π^2s cycloaddition of the in situ generated spiro[cyclohexa-2,4-diene-oxiran]one is reported. Further transformation of 11 to a variety of endo-tricyclo[5.2.2.0^2,6]undecanes (20, 25, 28, 30 and 31) and their photochemical behaviour upon singlet (¹S) excitation is described. Direct excitation of all the tricyclic chromophoric systems in benzene neatly furnished the protoilludanoids 32–36.