Photoinduced Molecular Transformations. part 147. [2+2]Photoaddition of Protected 4-Hydroxy-1(2H)-isoquinolinone with an Electrondeficient Alkene and the Formation of a 3,6-Epoxy-3,4,5,6-tetrahydro-2-benzazocin-1(2H)-one via a b-Scission of Cyclobutanoxyl Radicals Generated from the Resulting photoadduct

Abstract

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, (1α, 2aα, 8bα)-(±)-1-cyano-1,2a,3,8b-tetrahydro-8b-hydroxy-3-methylcyclobut[c]-isoquinolin-4(2H)-one and its (1α, 2aβ, 8bβ)- isomer in 78 and 67% yields. The photolysis of the hypoiodite generated in situ from the (1α, 2aα, 8bα)-(±)-cyclobutanol with mercury(II) oxide ― iodine in benzene induced a regioselective β-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