Diastereoselective photoaddition of methanol to (R)-(+)-limonene

Abstract

Extremely high diasteremeric excess was achieved from the photosensitized polar addition of methanol to (R)-(+)-limonene. Factors controlling the product``s de were extensively surveyed by structure of sensitizers, solvent polarity, and irradiation temperatures. The diastereomeric excesses (de``s) can be converted by changing solvent polarity, reaction temperature, and structure of sensitizers. The increased with lowering solvent polarity and decreased the irradiation temperature increased the diastereomeric excesses. Singlet sensitizer gave higher diastereomeric excess than triplet sensitizer. Methyl benzoate sensitizer in diethyl ether-0.5M methanol solution at -75℃ gave the highest de value of 96.3%.