Ramberg-Baecklund Reaction of 1,3-Dibromo-1H,3H-naphthothiopyran 2,2-Dioxide. Formation of Acenaphthyne Intermediate

Article abstract of DOI:10.1021/jo00149a013

Radical bromination of 1H,3H-naphtho<1,8-cd>thiopyran 2,2-dioxide (15) gave the corresponding monobromo sulfone 16 (48percent), dibromo sulfone 12 (43percent; cis/trans = 64/36), and tribromo sulfone 17 (5percent).Ramberg-Baecklund reaction of 12 was investigated under a variety of coditions with expectation of the formation of thiirene dioxide 11 from which generation of acenaphthyne (5) would be expected both thermally and photochemically.Observed characteristic features of the reaction are as follows: (i) the use of triethylamine as base yielded 1-bromo-acenaphthylene (20; 39percent) and debrominated products 15 (5percent) and 16 (9percent); (ii) the use of sodium methoxide as base afforded decacyclene (3) surprisingly, though in a trace amount, in addition to 20 (75percent) and acenaphthylene (18; 9percent); (iii) the use of potassium tert-butoxide as base gave an improved yield of 3 (5percent) along with 20 (36percent) and 18 (27percent).The formation of 3 may best be rationalized by assuming the generation of acenaphthyne intermediate 5 from 11 by loss of sulfur dioxide.