Photoisomerisation of bicyclo[4.2.0]octadienes to tricyclo[4.2.0.02,5] octenes: Application to the synthesis of [n]ladderanes

Article abstract of DOI:10.1016/S0040-4039(00)75854-0

A new approach for the extension of [n]ladderanes is described which involves formation of an end-fused bicyclo[4.2.0]octadiene and its photoisomerisation to the related tricyclo[4.2.0.0^2,5] octene as the ladderane extension step. The protocol is illustrated with the synthesis of [3]ladderane (9) from an unsubstituted cyclobutene and nor[5]ladderane (13) from an ester activated cyclobutene. The exo-stereochemistry of (13) is confirmed by reference to intermediate (23) for which a single crystal X-Ray structure analysis was obtained.