Total synthesis of (+/-)-2-isocyanoallopupukeanane

Abstract

2-Isocyanoallopupukeanane (4) has been obtained in racemic form from methyl 2-exo-methylbicyclo-[2.2.1]hept-5-ene-2-endo-carboxylate via dibromocarbene addition, S(N)2' displacement, chain extension, and elaboration of the unsaturated ketone 12c which underwent an intramolecular hetero-Diels-Alder reaction to afford 13 containing all the skeletal carbon atoms. The dihydropyran unit was cleaved by ozonolysis to give the tricarbocyclic intermediate which required seven more steps to complete the synthesis.