Type II photoreactions of α-alkyl β-oxoesters. Neighboring group effect on 1,4-biradical reactions and effective internal filter effect by the type II photoproduct
作者:Tadashi Hasegawa、Yoshiaki Arata、Masaru Endoh、Michikazu Yoshioka
DOI:10.1016/s0040-4020(01)96480-4
日期:1985.1
The α-alkyl β-oxoesters 1 undergo type II photoreactions. The process of back hydrogen transfer in the 1,4-biradical intermediate to revert to the starting ester is suppressed because of the intramolecular hydrogen bonding between the hydroxyl and carboalkoxyl groups in the biradical intermediate. The hydrogen bonding determines the stereochemistry of 1,4-biradical cyclization. The cyclobutanols having
α-烷基β-氧酸酯1经历II型光反应。由于双自由基中间体中的羟基和碳烷氧基之间存在分子内氢键,因此抑制了在1,4-双自由基中间体中向后氢转移以还原为起始酯的过程。氢键决定了1,4-双自由基环化的立体化学。羧基烷氧基具有顺式羟基的环丁醇仅由α-烷基β-氧代酸酯1形成。II型消除产物的烯醇形式苯甲酰乙酸2充当α的光反应的有效内部过滤器-烷基β-氧代酸酯1。