An efficient synthesis of benzofurans and their application in the preparation of natural products of the genus Calea
作者:María del Carmen Cruz、Joaquín Tamariz
DOI:10.1016/j.tet.2005.08.015
日期:2005.10
catalyzed by Lewis acids leads to a short and novel synthesis of benzofurans 2a–2f. When the olefins 4-dimethylamino-3-aryloxy-3-buten-2-ones 4a–4f were used, the cyclization process was faster and provided the corresponding substituted 2-acetylbenzofurans 1a–1f. Among the latter, naturally occurring compounds calebertin (1a), caleprunin A (1b), and caleprunin B (1c) were prepared in good overall yields.
Lewis酸催化的β-取代烯烃2-芳氧基-3-二甲基氨基丙酸甲酯3a - 3f的分子内环化反应导致短而新颖的苯并呋喃2a - 2f的合成。当使用烯烃4-二甲基氨基-3-芳氧基-3-丁烯-2-酮4a – 4f时,环化过程更快,并提供了相应的取代的2-乙酰基苯并呋喃1a – 1f。在后者中,天然存在的化合物calebertin(1a),caleprunin A(1b)和caleprunin B(1c)以较高的总收率制备。这些苯并呋喃还可以通过在前驱体中用DMFDMA对前体1-芳氧基丙烷-2-酮7a - 7c进行MW辐射直接处理,然后添加催化剂而得到,从而使路线缩短了一个步骤。