Abstract
As a fundamental experiment for the synthesis of 2-thiabulenes (10), syntheses of 2-thiaazulen-6-ones and 2-thiaazulenylium salts were attempted. For the synthesis of 2-thiaazulen-6-ones, a modified method was established for known compounds (12 and 15), and 1, 3-dihalogeno-5, 7-dimethyl-2-thiaazulen-6-ones (18 and 19) were successfully synthesized. Synthesis of 2, 5-dihalogeno-3, 4-diformylthiophenes, the starting materials for the synthesis of 1, 3-dihalogeno derivatives, by oxidation was accompanied by side reactions and their yield was generally poor. Therefore, 18 and 19 were synthesized by mercuration-halogenation of 5, 7-dimethyl-2-thiaazulen-6-one (14). For the synthesis of 2-thiaazulenylium salts, an attempt was first made to obtain 6-phenyl derivative by the application of phenyllithium to thiaazulenones (14 and 15). While 1, 2-addition product (47) was obtained from 14, 1, 2-additive (51) and 1, 4-additive (16) products were obtained from 15. Reaction of 1, 3-dibromo derivative (18) with phenyllithium resulted in halogen-metal interconversion of the bromine atom and the resultant lithio compound was yielded a compound (56) by the reaction of another molecule of 18. In the reaction of 18 with 2 moles of phenylmagnesium bromide, a normal addition product (58) was formed but the use of 11 moles resulted in the formation of an abnormal product (59) besides 58. Reduction of 18 with lithium aluminum hydride to obtain 64 ended in the liberation of bromine in 1-and 3-positions, and reduction without debromination was effected by the use of sodium borohydride. The alcohols (58 and 64) thereby obtained were isolated as their hexachloroantimonates (63 and 67) by treatment with hydrochloric acid and antimony pentachloride. 58 was also obtained as its perchlorate (60). Some discussions were made on the mechanism of the formation of 58 and 59.
