Pauson-Khand Adducts of N-Boc-propargylamine: A New Approach to 415-Disubstituted Cyclopentenones

A new approach to the synthesis of 4,5-disubstituted cyclopentenones is described. The strategy is based on the Pauson-Khand (PK) reaction of norbornadiene and N-Boc-propargylamine as an alkyne with a masked leaving group, which can be eliminated at will. This approach to the synthesis of 4,5-disubstituted cyclopentenones overcomes the problem of using the alkylation to introduce the alpha side chain. As an example, prostane 13-epi-12-oxo-phytodienoic acid (13-epi-12-oxo-PDA) methyl ester was synthesized.