Superelectrophiles, Formed in Superacids.

picet - spengler反应是一种酸催化的2-芳基乙胺中间亚胺分子内环化生成1,2,3,4-四氢异喹啉的反应，长期以来一直局限于具有强给电子基团的活性底物，如环苯环上的甲氧基或羟基。本文介绍了超酸催化2-苯乙胺亚胺的Pictet-Spengler反应，包括n -亚甲基-2-苯乙胺的原型Pictet-Spengler反应，以中高收率得到母体和1-取代的1,2,3,4-四氢异喹啉。产率取决于介质的酸度。在N-亚甲基-2-苯乙胺和相关亚胺的动力学研究中，发现环化速率与反应介质的酸度之间存在线性关系，有力地支持了N-质子化亚胺的额外质子活化的干预，即，指示超亲电试剂N，N-二质子化亚胺（氨-羰基指示）的参与。芳基乙烯基酮的纳扎罗夫式环化需要强酸性条件，尽管与纳扎罗夫反应的化学类比表面上意味着o -质子化单阳离子的直接电环化反应。本文描述了超强酸催化1-苯基-2-丙烯-1- 1的原型环化反应。动力学测量显示，这些环化反应的酸度依赖性强烈表明，参与的是O，O-双质子化而不是O-质子化单质子化。也就是说，1-苯基-2-丙烯-1- 1的环化代表了氧-羰基的电环化。我们还描述了取代基在1-苯基-2-丙烯-1- 1- 2位置的影响。基于密度泛函理论的从头计算支持了阳离子电循环比单离子电循环在能量上更有利的观点。

The Pictet-Spengler reaction, an acid-catalyzed intramolecular cyclization of intermediate imines of 2-arylethylamine to give 1,2,3,4-tetrahydroisoquinolines, has long been limited to active substrates which bear strongly electron-donating groups such as a methoxy or a hydroxy group on the cyclizing benzene ring. In this paper, we present superacid-catalyzed Pictet-Spengler reactions of imines of 2-phenethylamine, including the prototype Pictet-Spengler reaction of N-methylene-2-phenethylamine, to give the parent and 1-substituted 1,2,3,4-tetrahydroisoquinolines in moderate to high yields. The yields are dependent on the acidity of the media. A linear relationship was found between the rate of the cyclization and the acidity of the reaction media in kinetic studies of N-methylene-2-phenethylamine and related imines, strongly supporting the intervention of an additional protonative activation of the N-protonated imines, that is, the involvement of dicationic superelectrophiles, N,N-diprotonated imines (ammonium-carbenium dications).Strongly acidic conditions are required to induce the Nazarov-type cyclization of arylvinyl ketones, although chemical analogy with the Nazarov reaction would superficially imply a straightforward electrocyclization reaction of the O-protonated monocation. In this paper we describe the superacid-catalyzed prototype cyclization of 1-phenyl-2-propen-1-ones. The acidity-dependence of these cyclization reactions as revealed by kinetic measurements strongly suggests the involvement of the O,O-diprotonated dication rather than the O-protonated monocation. That is, the cyclization of 1-phenyl-2-propen-1-ones represents an electrocyclization of the oxonium-carbenium dication. We also describe the effect of substituents at the 2 position of 1-phenyl-2-propen-1-ones. Ab initio calculations, based on the density functional theory, support the idea that electrocyclzation of the dication is energetically more favorable than that of the monocation.