The photochemistry of 2,2-dimethyl- and 2-aryl-2-methylnaphthalen-1(2H)-ones. Substitution requirement for the oxadi-π-methane rearrangement

Abstract

The photochemistry of 2-aryl-2-methylnaphthalen-1(2H)-ones (1) and (2), 2,2-dimethylnaphthalen-1(2H)-one (6), 2,2,3-trimethylnaphthalen-1(2H)-one (7), 2,2,4-trimethylnaphthalen-1 (2H)-one (3), 2-(p-methoxyphenyl)-2,4-dimethylnaphthalen-1(2H)-one (8), and 2,2,5,7-tetramethylnaphthalen-1(2H)-one (12) has been examined. The compounds which did not contain a 4-substituent, (1), (2), (6), and (7), were virtually unchanged under conditions which caused the 4-methyl derivative (3) to undergo an oxadi-π-methane (ODPM) rearrangement to the 1,1a-dihydrocycloprop[a]indenone (4). Similar reactivity was shown by the 4-methyl derivative (8), which gave the ODPM rearrangement products (9) and (10). On further irradiation, both (9) and (10) underwent rearrangement to 4-(p-methoxyphenyl)-3,4-dimethylnaphthalen-1(4H)-one (11). The 4-methyl group in (3) and (8) would appear to be exerting a steric effect, since irradiation of 2,2,5,7-tetramethylnaphthalen-1(2H)-one (12) produced the 1-naphthol (13) and the 1-tetralone (14), both of which arise from further reaction of an ODPM rearrangement product. Syntheses of the naphthalen-1(2H)-ones (1), (8), and (12) are reported.