Studies related to cyclopentanoid natural products. Part 3. Synthesis of pentenomycin and its racemate

Abstract

(4R)-4-Benzyloxy-2-benzyloxymethylcyclopent-2-en-1-one (9b) reacted with osmium(VIII) oxide to give (2S,3S,4R)-4-benzyloxy-2-benzyloxymethyl-2,3-dihydroxycyclopentan-1-one (8b), the cis-hydroxylation occurring anti to the 4-benzyloxy group. By a hydrogenolysis–dehydration sequence, compound (8b) was converted into pentenomycin (1a).

Although the optical rotations of the synthetic pentenomycin (1a) and its 4,5,6-tri-O-acetyl, 2-bromo-4,5,6-tri-O-acetyl, and 6-O-benzyl derivatives (13a), (13b), and (1d), were substantially different from those reported in the literature, the compounds were shown to be enantiomerically pure.

When treated with t-butyldimethylsilyl chloride, (8R)-8-hydroxy-6-hydroxymethyl-1,4-thiaspiro-[4.4]non-6-ene (10b) was converted into its disilyl ether (10f). The last-cited compound reacted with benzeneseleninic anhydride to give (4R)-4-t-butyldimethylsilyloxy-2-t-butyldimethylsilyloxymethyl-cyclopent-2-en-1-one (9d), which was converted into pentenomycin (1a) by sequential reactions involving osmium(VIII) oxide and hydrochloric acid.

The racemate of compound (9d), prepared from the racemate of 4-hydroxy-2-hydroxymethyl-cyclopent-2-en-1-one(9c) by reaction with t-butyldimethylsilyl chloride, was similarly transformed into the racemate of pentenomycin (1a).