Syntheses of salvilenone and related compounds: II. A novel rearrangement of a tetrahydrophenalenone to a naphthopyranone

The reaction of isopropenyl carbinol ( 2 ) with aqueous hydrobromic acid and hydroiodie acid gave salvilenone ( 1 ) and naphthopyranone ( 3 ) respectively. The reaction mechanism has been investigated. The formation of ( 3 ) was undergone a novel rearrangement of a tetrahydrophenalenone to a naphthopyranone.