Trihaloacetylated Enol Ethers - General Synthetic Procedure and Heterocyclic Ring Closure Reactions with Hydroxylamine
作者:Agenor Colla、Marcos A. P. Martins、Günter Clar、Siegfried Krimmer、Peter Fischer
DOI:10.1055/s-1991-26501
日期:——
An improved procedure is described for preparing ß-trichloro- and ß-trifluoroacetyl derivatives of six simple enol ethers, in analytically pure form, high yield, and on an up to molar scale. The 4-alkoxy-1,1,1-trichloro [fluoro]-3-alken-2-ones 4a-c and 5a-c, thus obtained, are cyclocondensed with hydroxylamine hydrochloride (in pyridine, 35°C to afford the 5-hydroxy-5-trichloro[fluoro]methyl-4,5-dihydroisoxazoles 6 and 7 in high yield. With cyclic substrates, i.e. the trihaloacetyl dihydrofurans and -2H-pyrans 4d, e and 5d, e, a competitive rearrangement reaction gives 3-cyano-2-hydroxy-2-trichloro[fluoro]methyltetrahydrofurans and -2H-pyrans 8 and 9, respectively. Direct condensation to a dihydroisoxazole prevails at 0°C (> 85% for 4d, 5d), rearrangement to the cyano compounds at higher temperatures (65-70°C, > 70%). Under either condition, the respective heterocycle may be isolated in > 60% yield (except for 6e).
描述了一种改进的方法,用于制备六种简单烯醇醚的 β-三氯-和 β-三氟乙酰基衍生物,其分析纯形式、高产率和高达摩尔规模。将由此获得的4-烷氧基-1,1,1-三氯[氟]-3-链烯-2-酮4a-c和5a-c与盐酸羟胺(在吡啶中,35℃)环缩合,得到5 -羟基-5-三氯[氟]甲基-4,5-二氢异恶唑 6 和 7 以高产率与环状底物,即三卤乙酰基二氢呋喃和 -2H-吡喃 4d, e 和 5d, e 进行竞争性重排反应,得到 3 -氰基-2-羟基-2-三氯[氟]甲基四氢呋喃和-2H-吡喃8和9分别在0°C下直接缩合为二氢异恶唑(4d、5d时> 85%),重排为氰基化合物。在较高温度下(65-70°C,> 70%),在任一条件下,各自的杂环都可以以> 60% 的产率分离(6e 除外)。