2-Arylmethylideneindolin-3-ones: stereochemistry and reduction with sodium borohydride

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Abstract
The synthesis of 2-arylmethylideneindolin-3-ones and their 1-substituted analogues is described. The syntheses of the latter, with some exceptions, produced mixtures of cis- and trans-isomers which were separated by preparative t.l.c.; the products were characterised by spectroscopic methods. The ratio of the isomers varied with the structure of the indolinone; an explanation in terms of the opposing effects of orbital overlap control and steric crowding in the reaction intermediates and products is suggested. Reduction of the indolinones with sodium borohydride led to benzylindoles via intermediate indolinols, which were isolated from two of the reactions. A mechanism is proposed which differs from the one already advanced by other workers.

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