A Synthesis of Mono- and Dimethoxy-1,2,3,4-tetrahydroisoquinolines via Pummerer Reaction: Effects of Methoxyl Groups on Intramolecular Cyclization.
作者:Tatsumi SHINOHARA、Akira TAKEDA、Jun TODA、Yoko UEDA、Michiyo KOHNO、Takehiro SANO
DOI:10.1248/cpb.46.918
日期:——
A synthesis of 1, 2, 3, 4-tetrahydroisoquinolines (TIQs)(23) with one and two methoxyl groups at various positions of the benzene ring was achieved via the intramolecular cyclization of N-(aryl)methyl-2-(phenylsulfinyl)ethylamines (9) using the Pummerer reaction as a key step. The reaction was carried out by using trifluoroacetic anhydride (TFAA)(method A) of TFAA-BF3·Et2O (method B). The cyclization to 4-SPhTIQs (11) proceeded effectively when the reaction center at the benzene ring was electronically activated by a methoxyl group. In the reaction of the sulfoxide (9e) having two OMe groups at ortho- and para-positions a different cyclization reaction leading to a benzothiazepine (12) was observed, indicating that the high nucleophilicity of the benzene ring caused the unexpected reaction prior to the cyclization to 4-SPhTIQ (11e). The route starting from methoxylated benzaldehydes (5) was proved to provide an efficient and convenient method of TIQ synthesis which should be complementary to the well known Pictet-Spengler method.
合成了1, 2, 3, 4-四氢异喹啉(TIQs)(23),在苯环的不同位置上含有一个或两个甲氧基,这一过程是通过N-(芳基) methyl-2-(苯基亚磺酰)乙胺(9)进行的,采用Pummerer反应作为关键步骤。反应使用了三氟乙酸酐(TFAA)(方法A)和TFAA-BF3·Et2O(方法B)。当苯环的反应中心被甲氧基电子激活时,4-SPhTIQs(11)的环化反应有效进行。在具有两个OMe基团的亚磺酰(9e)反应中,观察到了一种不同的环化反应,形成了苯并噻嗪啉(12),这表明苯环的高亲核性导致了在环化到4-SPhTIQ(11e)之前发生了意想不到的反应。以甲氧基化苯甲醛(5)为起点的合成路线被证明是一种有效便捷的TIQ合成方法,应该与众所周知的Pictet-Spengler方法相辅相成。