A range of a-tocopherol analogues of varying side-chain length and structure
has been prepared by the Wittig reaction of alkyltriphenylphosphonium bromides
with either 6-benzyloxy-2,5,7,8-tetramethylchroman- 2-carbaldehyde (8) or
6-acetoxy-2,5,7,8-tetramethylchroman-2-carbaldehyde (14). These analogues
include 2-hexyl-2,5,7,8-tetramethylchroman-6-ol (11),
2-heptyl-2,5,7,8-tetramethylchroman-6-ol (12) and
2,5,7,8-tetramethyl-2-(pent-1-enyl)chroman-6-ol (15). Methoxycarbonylmethyl
6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (2) was formed by reaction
of the triethylammonium salt of trolox (1) with methyl bromoacetate. Reaction
of methoxycarbonylmethyltriphenylphosphonium bromide (16) with (8) did not
produce the expected methyl
3-(6-benzyloxy-2,5,7,8-tetramethylchroman-2-yl)prop-2-enoate (17), but rather
4-(6-benzyloxy-2,5,7,8-tetramethylchroman-2-yl)but-3-en-2-one (22). A proposed
mechanism for this unusual reaction is discussed.
一系列具有不同侧链长度和结构的生育酚类似物
是通过烷基三苯基溴化膦与 6-苄氧基-2,5,7,8-四甲基苯并吡喃-2-甲醛 (8) 的威蒂希反应制备的。
与 6-苄氧基-2,5,7,8-四甲基苯并吡喃-2-甲醛(8)或
6-乙酰氧基-2,5,7,8-四甲基苯并二氢吡喃-2-甲醛(14)发生反应。这些类似物
包括 2-己基-2,5,7,8-四甲基苯并二氢吡喃-6-醇(11)、
2-庚基-2,5,7,8-四甲基苯并二氢吡喃-6-醇(12)和
2,5,7,8-tetramethyl-2-(pent-1-enyl)chroman-6-ol (15).甲氧羰基甲基
6-羟基-2,5,7,8-四甲基苯并二氢吡喃-2-甲酸甲氧羰基甲基酯(2)是通过以下反应生成的
的三乙基铵盐与溴乙酸甲酯反应生成。反应
甲氧羰基甲基三苯基膦溴化物(16)与(8)反应并没有产生预期的甲基溴。
生成预期的甲基
3-(6-苄氧基-2,5,7,8-四甲基苯并二氢吡喃-2-基)丙-2-烯酸甲酯 (17),而是
4-(6-benzyloxy-2,5,7,8-tetramethylchroman-2-yl)but-3-en-2-one (22).本文讨论了这一不寻常反应的
讨论了这一不寻常反应的机理。