C,O-Dialkylation of Meldrum's Acid: Synthesis and Reactivity of 1,3,7,7-Tetramethyl-4<i>H</i>,10<i>H</i>-6,8,9-trioxa-2-thiabenz[<i>f</i>]azulen-5-one
作者:Chad A. Snyder、John P. Selegue、Eniolami Dosunmu、Nathan C. Tice、Sean Parkin
DOI:10.1021/jo034708i
日期:2003.9.1
6-dio ne (8), result in the formation of 1,3-dimethyl-7,8-dihydro-4H-thieno[3,4-c]oxepin-6-one (6). The transformation occurs via a retro-Diels-Alder elimination of acetone followed by hydrolysis and decarboxylation of the resulting ketene. The ketene is trapped by tert-butyl alcohol, furnishing 1,3-dimethyl-6-oxo-7,8-dihydro-4H,6H-thieno[3,4-c]oxepine-7-carboxylic acid tert-butyl ester (7). All compounds
麦德鲁姆酸与3,4-双(氯甲基)-2,5-二甲基噻吩(1)或3,4-双(溴甲基)-2,5-二甲基噻吩(2)的反应产生了动力学上有利的C,O-二烷基化产物,1,3,7,7-四甲基-4H,10H-6,8,9-三恶唑-2-噻吩并[f] azulen-5-one(4)。从回流的甲醇中重结晶4得到甲醇裂解产物5-(4-甲氧基甲基-2,5-二甲基噻吩-3-基甲基)-2,2-二甲基[1,3]二恶烷-4,6-二酮(5)。尝试将4异构化为热力学上有利的C,C-二烷基化产物1,1,3-二甲基-5,6-二氢-4H-环戊[c]噻吩(2-螺基-5)2,2-二甲基-4,6 -二烯(8),导致形成1,3-二甲基-7,8-二氢-4H-噻吩并[3,4-c] oxepin-6-一(6)。该转化通过逆Diels-Alder消除丙酮,然后水解和脱羧得到的乙烯酮而发生。乙烯酮被叔丁醇捕获,得到1,3-二甲基-6-氧代-7,8-二氢-4H,6H-噻吩并[3