Catalytic Asymetric Hydrogenation of Heteroaromatics

点击翻译按钮获取中文摘要

1. Catalytic Hydrogenation of Heteroaromatic Compounds using Transition Metal ComplexWe found that rhodium complex generated from Rh (acac)(cod) and triphenylphosphine exhibited high catalytic activity for hydrogenation of indoles. The rhodium catalyst was also effective in hydrogenation of other 5-membered heteroaromatic compounds.2. Catalytic Asymmetric Hydrogenation of 2-Substituted IndolesThe hydrogenation of N-acetyl-2-butylindole proceeded in the presence of cataionic (S, S)-(R,R)-PhTRAP-rhodium complex and cesium carbonate, giving (R)-N-acetyl-2-butylindoline with 94% ee in 92% isolated yield. This reaction is the first example of highly enantioselective hydrogenation of 5-membered heteroaromatic compounds. The chiral catalyst showed high enantioselectivity for the hydrogenation of other 2-substituted indoles (up to 95% ee).3. Catalytic Asymmetric Hydrogenation of 3-Substituted IndolesThe chiral PhTRAP-rhodium catalyst exhibited good enantioselectivity (86% ee) for the hydrogenation of N-acetyl-3-methylindole, but the reaction was accompanied by serious alcoholysis of N-acetyl group. p-Toluenesulfonyl group is the protective group on nitrogen of choice in asymmetric hydrogenation of 3-substituted indoles. The hydrogenation of 3-methyl-N-p-toluenesulfonylindole gave the corresponding indoline with 98% ee in 93% isolated yield.