Regio- and Diastereoselectivity in the Reaction Sequence from Secondary 3-Oxa-5-hexen-1-ylamines to Bicyclic Compounds via Nitrones
作者:Hans Aurich、Michael Geiger、Ulrich Sievers
DOI:10.1055/s-1997-938
日期:1997.8
Secondary amines 2 and 8 are oxidized by hydrogen peroxide in the presence of sodium tungstate providing nitrones. If the amino function is substituted by one primary and one secondary alkyl moiety, oxidation proceeds with high regioselectivity at the primary alkyl group affording aldonitrones. Thus, compound 2b gives exclusively 3b that undergoes an intramolecular cycloaddition yielding 4b. From 2c, however, in addition to 4c nitrone 5 is formed as by-product, which affords the bridged compound 6 on heating in toluene. Oxidation of compounds 8 yields nitrones 9 which are converted to bridged compounds 10 as major products along with small amounts of regioisomers 11 at elevated temperatures. The intramolecular cycloaddition of the chiral nitrones 3b and c as well as 9b proceeds with high diastereoselectivity.
仲胺 2 和 8 在钨酸钠存在下被过氧化氢氧化,生成亚硝基脲。如果氨基被一个伯烷基和一个仲烷基取代,则伯烷基上的氧化反应会以高区域选择性进行,生成醛基硝基膦。因此,化合物 2b 只生成 3b,3b 经过分子内环加成反应生成 4b。然而,从 2c 中除了生成 4c 之外,还生成了副产物硝酮 5,在甲苯中加热后可得到架桥化合物 6。化合物 8 氧化生成硝酮 9,硝酮 9 在高温下转化为桥接化合物 10 作为主要产物,同时还生成少量的区域异构体 11。手性硝基腈 3b 和 c 以及 9b 的分子内环加成反应具有很高的非对映选择性。