Trifluoroacetic acid catalysed Claisen rearrangement of 5-allyloxy-2-hydroxybenzoic acid and esters: an efficient synthesis of (±)-mellein
作者:Laurence M. Harwood
DOI:10.1039/c39820001120
日期:——
5-Allyloxy-2-hydroxybenzoic acid (1a) and the esters (1b–f) in refluxing trifluoroacetic acid are smoothly converted into 3,4-dihydro-5,8-dihydroxy-3-methylisocoumarin (3) and the corresponding 4-alkoxycarbonyl 2,3-dihydro-5-hydroxy-2-methylbenzofurans (4a–f)via regioselective Claisen rearrangement to the 6-position of the aromatic nucleus with subsequent acid catalysed cyclisation.
在回流的三氟乙酸中,将5-烯丙氧基-2-羟基苯甲酸(1a)和酯(1b - f)平稳地转化为3,4-二氢-5,8-二羟基-3-甲基异香豆素(3)和相应的4-烷氧基羰基2,3-二氢-5-羟基-2-甲基苯并呋喃(4a – f)通过区域选择性Claisen重排至芳核的6位,随后进行酸催化的环化反应。