A Partial Synthesis of (−)-Shinjulactone H from (+)-Quassin

A partial synthesis of (—)-shinjulactone H (3) from (+)-quassin (1) required the selective manipulation of two similar O-methyldiosphenol groups. Protection of the δ-lactone in 1 as an ortho ester, selective reduction of the C-1 carbonyl group, hydrolysis of the resulting enol ether in the A ring, and catalytic hydrogenation of the O-methyldiosphenol in the C ring delivered an intermediate possessing an α-ketol group in the A ring and an α-methoxy ketone group in the C ring. Demethylation and concomitant α-ketol tautomerization in the A ring delivered (-)-shinjulactone H (3).