Effects of Aromatic Substituents on the Photocleavage of 1-Acyl-7-nitroindolines

Photolysis of 1-acyl-7-nitroindolines in aqueous solution gives a carboxylic acid and a 7-nitrosoindole. These compounds are useful as photolabile precursors of carboxylic acids, particularly neuroactive amino acids. The effect of electron-donating substituents at the 4-position has been explored for its effect on photolysis efficiency. 4-Methoxy substitution improved the photolysis efficiency >2-fold but the 4-dimethylamino analogue was essentially inert. A 5-alkyl substituent, that blocks unwanted nitration at this position, reduced the beneficial effect of the 4-methoxy group.