Selective synthesis of monomethyltocols viaη-allylnickel complexes

Abstract

A new synthesis of the monomethyltocols (1a–c) and the 2,2-dimethylchroman-6-ol models (2a–c), using the di-µ-bromobis-(1–3-η-3-alkylbut-2-enylnickel) complexes (9a and b), is described. Reaction of the η-allyl-nickel complexes (9a and b) with the bromo-p-diacetoxytoluenes (3a–c) gave the corresponding alkyl substituted p-diacetoxytoluenes (10a–c) and (11a–c) in high yield, and these were converted into the chromanols (1a–c) and (2a–c) by hydrolysis–cyclisation with tin(II) chloride and hydrochloric acid, also in high yield.