SYNTHESIS OF ALPHA-TOCOPHEROL ANALOGS

A range of alpha-tocopherol analogues of varying side-chain length and structure has been prepared by the Wittig reaction of alkyltriphenylp hosphonium bromides with either enzyloxy-2,5,7,8-tetramethylchroman-2- carbaldehyde (8) or -acetoxy-2,5,7,8-tetramethylchroman-2-carbaldehyde (14). These analogues include 2-hexyl-2,5,7,8-tetramethylchroman-6-ol (II), 2-heptyl-2,5,7,8-tetramethylchroman-6-ol (12) and 2,5,7,8-tetra methyl-2-(pent-1-enyl)chroman-6-ol (15). Methoxycarbonylmethyl 6-hydro xy-2,5,7,8-tetramethylchroman-2-carboxylate (2) was formed by reaction of the triethylammonium salt of trolox (I) with methyl bromoacetate. Reaction of methoxycarbonylmethyltriphenylphosphonium bromide (16) wit h (8) did not produce the expected methyl loxy-2,5,7,8-tetramethylchro man-2-yl)prop-2-enoate (17), but rather oxy-2,5,7,8-tetramethylchroman -2-yl)but-3-en-2-one (22). A proposed mechanism for this unusual react ion is discussed.