Highly efficient indium(<scp>iii</scp>)-mediated cyclisation of 5-hydroxy-1,3-diketones to 2,3-dihydro-4H-pyran-4-ones; mechanistic insights from in situFourier transform infrared spectroscopy
作者:Philip C. Andrews、William J. Gee、Peter C. Junk、Harald Krautscheid
DOI:10.1039/b919402a
日期:——
5-Hydroxy-1,3-diketones have been synthesised in a facile one-pot reaction from the treatment of acid chlorides with non-substituted ketones and LiHMDS. Subsequent cyclisation to 2,3-dihydro-4H-pyran-4-ones occurs rapidly and in high yield (89–99%) when mediated by anhydrous indium(III) chloride. A spectroscopic study of the reaction using in situ Fourier transform infrared (FTIR) spectroscopy has shown the reaction to be highly dependent on temperature, metal complex formation and InCl3 concentration. Since the reaction is deactivated by the precipitation of [InCl3·(H2O)3], the concurrent use of a stronger drying agent, such as molecular sieves 4 Å or anhydrous MgSO4, allows the reaction to be successfully carried out at relatively low loadings of InCl3 (1–10%). In their absence, the optimum reaction conditions were found to be a diketone : InCl3 ratio of 3 : 1 in toluene, and a reaction temperature of 80 °C.
5-羟基-1,3-二酮通过将酸氯化物与非取代的酮和LiHMDS在简单的一锅反应中合成。随后在无水氯化铟(III)的催化下快速且高产率(89-99%)发生环化反应生成2,3-二氢-4H-吡喃-4-酮。对该反应的光谱学研究表明,反应高度依赖于温度、金属络合物的形成以及InCl3的浓度。由于反应会因[InCl3·(H2O)3]的沉淀而失活,因此同时使用更强的干燥剂,如4Å分子筛或无水MgSO4,可以使反应在相对低的InCl3负载(1-10%)下成功进行。在没有这些干燥剂的情况下,发现最佳反应条件为二酮与InCl3的摩尔比为3:1,溶剂为甲苯,反应温度为80°C。