Photocyclization reactions. Part<b>7</b>. Solvent and substituent effects in the synthesis of dihydrobenzofuranols using photocyclization of α-(2-acylphenoxy)toluenes and ethyl 2-acylphenoxyacetates
作者:Essam Mohamed Sharshira、Takaaki Horaguchi
DOI:10.1002/jhet.5570340634
日期:1997.11
Photocyclization reactions were carried out on α-(2-acylphenoxy)toluenes 1a-e and 2-acylphenoxy-acetates 2a-e in three solvents of different polarity (benzene, acetonitrile and methanol) to examine solvent and substituent effects on the cyclization of 1,5-biradical intermediates to dihydrobenzofuranols. Irradiation of 1a-e in benzene gave cis-dihydrobenzofuranols cis-4b-e selectively in 14-84% yields
在三种极性不同的溶剂(苯,乙腈和甲醇)中,对α-(2-酰基苯氧基)甲苯1a-e和2-酰基苯氧基乙酸酯2a-e进行光环化反应,以检查溶剂和取代基对1环化的影响,是二氢苯并呋喃醇的5-双自由基中间体。在苯中辐照1a-e可以选择性地以14-84%的收率与重排的产物2-酰基二苯甲酮5b-d(23-39%)一起产生顺式-二氢苯并呋喃醇顺式4b-e。La-e在乙腈或甲醇中的光环化反应生成eis-和反式-二氢苯并呋喃醇4a-e的混合物产率为28-81%,少量的2-酰基二苯甲酮5b-c产率为6-12%。在极性乙腈或甲醇中,二氢苯并呋喃醇的顺式和反式立体选择性降低。立体选择性的降低归因于1,5-双自由基的羟基与溶剂之间的分子间氢键。另一方面,在苯中的酯2a-e的辐射选择性地以48-74%的产率提供了顺式-二氢苯并呋喃醇顺式-13a -e。类似地,2a-e在乙腈或甲醇中的光环化反应以相当高的收率产生了二氢苯并