Selective Intermolecular Photo-[4 + 4]-cycloaddition with 2-Pyridone Mixtures. 3. Synthetic Transformations of the Trans Cross-Product (1α,2β,5β,6α)-3-Butyl-9- methoxy-3,7-diazatricyclo[4.2.2.2^2,5]dodeca-9,11-diene-4,8-dione

Abstract

Transformations of the tricyclic product 3 derived from [4 + 4] photocycloaddition of N-butyl-2-pyridone with 4-methoxy-2-pyridone has demonstrated, for the first time, facile opening of the secondary lactam after activation of the amide nitrogen with a tert-butyl carboxylate (Boc) group. Methanolysis and lithium borohydride reduction both result in opening of the amide group under very mild conditions to give 21 and 24, respectively. Concomitant reduction of a ketone derived from hydrolysis of the enol ether sets an additional stereogenic center in 24 with complete stereogenic control. These reactions illustrate the synthetic potential of the 2-pyridone photocycloaddition products, generating a cyclooctene as a single isomer, with functionality at seven carbons and five stereogenic centers