Method for manufacturing 3-isochromanone

The present invention intends to provide a method for producing 3-isochromanones represented by formula (II) useful as a synthetic starting material of medicals or agricultural chemicals and the cyano compound represented by formula (I) by an industrially advantageous method in a high yield. Disclosed herein is a method for manufacturing a 3-isochromanone represented by the following formula (II): (wherein R2, R3, R4 and R5 each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group), said method is characterized by comprising the steps of: hydrolyzing a cyano compound represented by formula (I): (wherein R1 represents a hydrogen atom, an alkyl group or an aryl group, and R2, R3, R4 and R5 have the same meanings as defined above) and subjecting the hydrolyzate to intramolecular cyclization. c