2 H -1,3-恶嗪和1 H-吡咯-3(2 H)-one通过温度依赖性Rh(II)-类胡萝卜素介导的2 H -azirine-ring扩展的选择性合成
摘要:
2-羰基取代的2 H-叠氮基与2-氰基-2-重氮乙酸乙酯或2-重氮-3,3,3-三氟丙酸酯的Rh(II)催化反应可轻松获得2 H -1,3 -恶嗪和1 H-吡咯-3(2 H)-ones 。这些化合物可以使用温度作为唯一变化的参数,从相同的原料中选择性制备。两种杂环产物的共同前体2-azabuta-1,3-diene中间体在动力学控制下异构化为2 H -1,3-恶嗪,而1 H -pyrrol-3(2 H)-一个是在高温下反应的唯一产物。根据DFT计算,一个原子的恶嗪环收缩涉及开环成2-azabuta-1,3-二烯中间体,然后发生1,5-和1,2-质子性位移,导致连续形成亚氨基酰亚胺基和甲亚胺叶立德,然后进一步进行环化为吡咯衍生物。
Rh2(OAc)4-catalyzed reaction of α-diazocarbonyl compounds with 2-carbonyl-substituted 2H-azirines
摘要:
The Rh-2(OAc)(4)-catalyzed reaction of 2H-azirine-2-carbaldehydes with dimethyl diazomalonate proceeds via azirinium ylide formation, isomerization to 2-azabuta-1,3-dienes followed by 1,6-pi-electrocyclization to give 2H-1,3-oxazines. According to DFT-calculations ring opening of azirinium ylides should occur stereoselectively to give 2-azadienes with the C=C bond exclusively in the Z configuration. Changing a formyl group for an acetyl group in the azirine leads to a lowering of stereoselectivity and the formation of azadienes with an E configuration of the C=C bond was observed. The reaction of 2-acy1-2-diazoacetates with 2H-azirine-2-carbaldehydes proceeds similarly, but the 2-acetyl-substituted 2H-1,3-oxazines formed are unstable under chromatographic purification and rearrange easily into pyrrole derivatives. (C) 2013 Elsevier Ltd. All rights reserved.