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Stereospecific Photochemical Ring Expansion of Lithiated Benzamides

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  • Ring Enlargement (Photochem.
  • Stereospecific Photochem. Ring Expansion Of Lithiated Benzamides)


Treatment of N-benzylbenzamides with a strong base (LDA or me3CLi) followed by irradn. with a 500 W tungsten lamp provides, according to the substitution pattern of the starting amides, either norcaradienes or cycloheptadienones by overall insertion of the N-benzyl group into the benzamide's arom. ring system. Chiral benzamides undergo the ring expansion with high (sometimes complete) stereospecificity. The reaction appears to occur via a series of pericyclic reactions (photochem. or thermal sigmatropic rearrangements and thermal electrocyclic reactions) following an initial dearomatizing cyclization. [on SciFinder (R)]

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