Journal of the American Chemical Society, Vol.117, No.10, 2698-2710, 1995
Novel and Efficient Azomethine Ylide Forming Photoreactions of N-(Silylmethyl)Phthalimides and Related Acid and Alcohol Derivatives
An investigation of the photochemistry of N-(silylmethyl)phthalimides and related alpha-phthaloylacetic acids and 2-phenylethanol derivatives has uncovered new excited state processes resulting in the formation of azomethine ylide intermediates. Irradiation of N-[(trimethylsilyl)methyl]phthalimide in MeCN promotes C to O silyl transfer to generate the corresponding azomethine ylide which is efficiently trapped by reaction with water to yield the N-methylphthalimide or by dipolar cycloaddition with acetone, methyl acrylate, or acrylonitrile. Cycloadditions with the latter two dipolarophiles are both regioselective and endo-stereoselective. These processes can be triplet photosensitized by use of acetophenone. The related N-[(trimethylsilyl)methyl]-1,8-naphthalimide reacts in a similar manner upon irradiation in MeCN solutions containing the dipolarophiles methyl acrylate and acrylonitrile to produce cycloadducts which undergo spontaneous elimination of TMSOH, yielding alpha,beta-unsaturated ester or nitrile products. The ylide formed by irradiation of the (silylmethyl)phthalimide is trapped in a stereospecific (retention) manner by the dipolarophiles trans-hex-4-en-3-one, dimethyl maleate, and dimethyl fumarate.