Highly Stereoselective and Flexible Synthesis of 6-Alkoxy-5,6-dihydro-4<i>H</i>-1,2-oxazines by Conjugate Addition of Organolithium Compounds to 6<i>H</i>-1,2-Oxazines Followed by Trapping with Electrophiles
作者:Hans-Ulrich Reissig、Monika Buchholz
DOI:10.1055/s-2002-33107
日期:——
additions of reactive organolithium compounds such as phenyllithium, n-butyllithium, tert-butyllithium, and 2-propenyllithium to 6H-1,2-oxazines 1, 24, and 25 followed by trapping of the intermediates with electrophiles gave a variety of highly substituted 6-alkoxy-5,6-dihydro-4H-1,2-oxazines 2-15 and 27-30 generally in very good yields. Most interestingly, this reaction sequence proceeds with high stereocontrol
将反应性有机锂化合物(如苯基锂、正丁基锂、叔丁基锂和 2-丙烯基锂)共轭加成到 6H-1,2-恶嗪 1、24 和 25,然后用亲电试剂捕获中间体,得到各种高度取代的6-alkoxy-5,6-dihydro-4H-1,2-oxazines 2-15 和 27-30 通常产率非常好。最有趣的是,该反应序列以高度立体控制进行,大量过量或仅产生反式、反式-非对映异构体。使用苯甲醛作为亲电子试剂,仅形成了化合物 8,它是八种可能的非对映异构体之一。甲基锂或锂化的甲氧基丙二烯作为亲核组分提供预期的加成产物 17 和 19,但对于这些反应性较低的有机锂化合物,双 1,2-恶嗪 18 和 20 的形成似乎是不可避免的。