Flash photolysis of 4-diazoisochroman-3-one in aqueous solution. Hydrationof the carbene produced by loss of nitrogen and ketonization of the enol hydration product

Flash photolysis of 4-diazoisochroman-3-one in aqueous solution resulted in loss of nitrogen and transient production of the alpha-carbonylcarbene 3-k etoisochroman-4-ylidene, the hydration of which generated a short-lived spe cies that was identified as the enol isomer of the lactone, 4-hydroxyisochr oman-3-one. This assignment is supported by x-ray crystallographic determin ation of the structure of the final lactone product, by the shape of the ra te profile for ketonization of the enol intermediate to the lactone, and by solvent isotope effects on, and the Form of acid-base catalysis of, the ke tonization reaction. Copyright (C) 2000 John Wiley & Sons, Ltd.