Novel formation of isomeric bicyclo[3.2.0]heptan-1-ols from phenyl vinyl sulfoxide and the cyclopentanone lithium enolate generated by conjugate addition of lithiated (E)-but-2-enyldiphenylphosphine oxide to 2-methylcyclopent-2-enone

Whereas the title enolate 2 in THF reacts at −10°C with 2 equiv of phenyl vinyl sulfone to provide the hydrindanol 9 (9%), it reacts with 1 equiv of phenyl vinyl sulfoxide to give 7-(phenylsulfinyl)bicyclo[3.2.0]heptan-1-ol sulfoxides 11 and 12 (50% overall) and adduct 10 (10%). The yield of the bicycloheptanols decreases to 35% in the dark and increases to 68% under irradiation. Their formation is entirely suppressed by HMPA. Stereochemistry of 12 was provided by X-ray crystallography of the derived sulfone 14. Base-induced ring opening of the sulfone in the presence of phenyl vinyl sulfone gives the alkylated cyclopentanones 17, 18, and 21 and the bicyclo[2.2.1]heptanone 20. The bicyclo[3.2.0]heptanols 11 and 12 are considered to arise by intramolecular nucleophilic or single electron transfer processes.