A Short, Oxetane-Based Synthesis of (±)-Sarracenin

(±)-Sarracenin (1) was synthesized in nine steps and six pots from the simple precursors acetaldehyde and cyclopentadiene. Paterno-Buchi photocycloaddition of this pair yielded two diastereomeric oxetanes (3x, 3n). The major, exo isomer underwent highly regioselective acid-catalyzed methanolysis at the methyl-bearing oxetane center to give a 3-cyclopentenol derivative (8). Attachment of a methyl 2-(2-phenylethenyl)ethanoate moiety, a 3-oxopropanoate equivalent, with inversion of the toluenesulfonate 9 derived from 8 gave a diene (11) containing all of the necessary carbon atoms. Following decarbomethoxylation, both olefins were simultaneously ozonized to an in situ equivalent of a trialdehyde (2) which has played a role in previous synthetic studies and biosynthetic postulates in this area. Spontaneous dehydration of 2 produced (±)-sarracenin in 18% overall yield from the tosylate 9, the first purified intermediate in the sequence.