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Title: Novel and Efficient Azomethine Ylid Forming Photoreactions of N-(Silylmethyl)phthalimides and Related Acid and Alcohol Derivatives
Authors: Yoon, U. C.;Kim, D. U.;Lee, C. W.;Choi, Y. S.;Lee, Yean-Jang;Ammon, H. L.;Mariano, P. S.
Contributors: 化學系
Date: 1995-03
Issue Date: 2012-12-10T02:51:22Z
Publisher: American Chemical Society
Abstract: An investigation of the photochemistry of N-(silylmethy1)phthalimides and related a-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 0 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-[ (trimethylsily1)methyll- 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 a,P-unsaturated ester or nitrile products.
The ylide formed by irradiation of the (silylmethy1)phthalimide is trapped in a stereospecific (retention) manner by
the dipolarophiles trans-hex-4-en-3-one, dimethyl maleate, and dimethyl fumarate. The effect of aryl ring substitution
on the regiochemical course of the photoinduced C to 0 silyl migration process was probed by use of the 4-methoxyand
4-carbomethoxyl-N-(silylmethyl)phthalimides. Irradiation of the former substance in an MeCN solution containing
acrylonitrile gives rise to a single adduct whose structure suggests that silyl migration to oxygen of the carbonyl
meta to the OMe substituent is highly favored. In contrast, the 4-carbomethoxyphthalimide is converted under these
conditions to a mixture of regioisomeric adducts. Thus, silyl migration in the excited state of this substance is
nonselective. In accord with hints found in earlier observations made by Kanaoka (Chem. Pham. Bull. 1982, 30,
1263), N-phthalimide derivatives of the a-amino acids glycine, alanine, and phenylalanine undergo similar ylide
forming photoreactions upon irradiation in MeCN solutions. The azomethine ylides produced by photodecarboxylation
of these substances are efficiently trapped by dipolarophiles, and the overall photoreactions starting with the alanine
and phenylalanine derivatives are highly stereoselective. Finally, the N-phthalimide derivative of 2-amino- 1 -
phenylethanol also is transformed to a related ylide upon irradiation in MeCN. The nature, regiochemical and
stereochemical course, and mechanistic interpretation of these new azomethine ylide forming photoreactions are
discussed in this publication.
Relation: J. Am. Chem. Soc., 117(10): 2698-2710
Appears in Collections:[化學系] 期刊論文

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