An Efficient and Simple Synthesis of 3,4,5,6-Tetrahydro-2<i>H</i>-1,2-oxazines by Sodium Cyanoborohydride Reduction of 5,6-Dihydro-4<i>H</i>-1,2-oxazines
作者:Reinhold Zimmer、Thomas Arnold、Kai Homann、Hans-Ulrich Reissig
DOI:10.1055/s-1994-25636
日期:——
3,4,5,6-Tetrahydro-2H-1,2-oxazines are prepared by reduction of the corresponding 5,6-dihydro-4H-1,2-oxazines with sodium cyanoborohydride as the reducing agent in acetic acid. This reaction gives the 3,5-disubstituted compounds 2a-c, 2f-g, and 5a,b with good to excellent cis selectivities, while a 3,6-disubstituted 1,2-oxazine leads to a trans configurated product as the major isomer. Under the same reaction conditions the bicyclic heterocycle 14 affords two products, the expected compound 15 and the cyclopentenol derivative 16 as a byproduct. Also, the formation of trifluoromethylated ketoximes 18 and 21 starting from the precursors 17 and 19 is described.
以氰基硼氢化钠为还原剂,在醋酸中还原相应的 5,6-二氢-4H-1,2-噁嗪,制备出 3,4,5,6-四氢-2H-1,2-噁嗪。该反应可得到 3,5-二取代的化合物 2a-c、2f-g 和 5a,b,顺式选择性良好,甚至极佳,而 3,6-二取代的 1,2-噁嗪会导致反式构型产物成为主要异构体。在相同的反应条件下,双环杂环 14 产生两种产物,即预期的化合物 15 和副产物环戊烯醇衍生物 16。此外,还介绍了由前体 17 和 19 生成三氟甲基酮肟 18 和 21 的过程。