Reactions of the cyclic tautomer of 3-indoleacetamides. Synthesis of Nb-methyl-4,5,6-tribromo-3-indoleacetamide.
作者:Tohru HINO、Hideya UEHARA、Mika TAKASHIMA、Tomohiko KAWATE、Hiroko SEKI、Ritsuko HARA、Tadao KURAMOCHI、Masako NAKAGAWA
DOI:10.1248/cpb.38.2632
日期:——
The cyclic tautomer (5) of Nb-methyl-3-indoleacetamide (4) has been prepared by dissolving 4 in phosphoric acid. The bromination of 5 with 1 or 2 mol of N-bromosuccinimide (NBS) or 2, 4, 4, 6-tetrabromo-2, 5-cyclohexadienone (TABCO) gave the 5-bromo- (8) and the 5, 7-dibromo (9) derivatives. On the other hand, the 5-bromo derivative (11) was the major product of the bromination of the N-acetyl cyclic tautomer (6) even with 2 mol of NBS. The 5-nitro derivative (17) was obtained in excellent yield by the nitration of 6 with ammonium nitrate in trifluoroacetic anhydride (TFAA). Reduction of 17 followed by bromination gave the 4, 6-dibromo derivative (19), which gave the tribromide (20) in the Sandmeyer reaction. The 4, 5, 6-tribromo-3-indoleacetamide (7), which is the indole moiety of a marine indole alkaloid, chartelline A, was obtained by the ring opening of 20. Furthermore, the oxidation of 5 with lead tetraacetate followed by acetylation gave the 5-acetoxy derivative (22). The selective hydrolysis and bromination of 22 gave the 4, 6-dibromo-5-hydroxy derivative (24).
通过在磷酸中溶解Nb-甲基-3-吲哚乙酰胺(4),制备了其循环互变异构体(5)。使用1或2摩尔的N-溴丁二酰亚胺(NBS)或2,4,4,6-四溴-2,5-环己二烯酮(TABCO)对5进行溴化,得到了5-溴(8)和5,7-二溴(9)衍生物。另一方面,即使使用2摩尔的NBS,N-乙酰循环互变异构体(6)的溴化主要产物也是5-溴衍生物(11)。通过在三氟乙酸酐(TFAA)中用硝酸铵对6进行硝化,得到了极佳产率的5-硝基衍生物(17)。随后对17进行还原和溴化,得到了4,6-二溴衍生物(19),后者在桑德迈耶反应中生成三溴化物(20)。通过20的开环反应得到了4,5,6-三溴-3-吲哚乙酰胺(7),这是海洋吲哚生物碱chartelline A的吲哚部分。此外,用四乙酸铅对5进行氧化,随后进行乙酰化,得到了5-乙酰氧基衍生物(22)。对22进行选择性水解和溴化,得到了4,6-二溴-5-羟基衍生物(24)。