PHOTOINDUCED MOLECULAR-TRANSFORMATIONS .147. [2+2] PHOTOADDITION OF PROTECTED 4-HYDROXY-1(2H)-ISOQUINOLINONE WITH AN ELECTRON-DEFICIENT ALKENE AND THE FORMATION OF A 3,6-EPOXY-3,4,5,6-TETRAHYDRO-2-BENZAZOCIN-1(2H)-ONE VIA A BETA-SCISSION OF CYCLOBUTANOXYL RADICALS GENERATED FROM THE RESULTING PHOTOADDUCT

The direct irradiation of 4-benzyloxycarbonyloxy-2-methyl-1(2H)-isoquinolinone gave a 1 to 1 ratio of two stereoisomers of [2+2] photoadducts in 97% yield. Removal of the protecting group from the adducts by hydrogenolysis gave the corresponding cyclobutanols, (1 alpha, 2a alpha, 8b alpha)-(+/-)-1-cyano-1,2a,3,8b-tetrahydro-8 b-hydroxy-3 -methylcyclobut[c]-isoquinolin-4(2H)-one and its (1 alpha, 2a beta, 8b beta)- isomer in 78 and 67% yields. The photolysis of the hypoiodite generated in situ from the (1 alpha, 2a alpha, 8b alpha)-(+/-)-cyclobutanol with mercury(II) oxide - iodine in benzene induced a regioselective beta-scission at the ring fusion bond of the cyclobutanoxyl radical to give 5-cyano-3,6-epoxy-3,4,5,6-tetrahydro-6-hydroxy-2-methyl-2- benzazocin-1(2H)-one in 76% yield. The cyano substituent and the amide nitrogen play a decisive role in directing the bond to be cleaved.