1H-indole-4-propanoic acid derivatives was examined as model construction for the A–B–C ringsystem of lysergic acid (1). Smooth cyclization from the 4 position of 1H-indole to the 3 position was achieved by Vilsmeier–Haack reaction in the presence of K2CO3 in MeCN, and the best substrate was found to be the N,N-dimethylcarboxamide 9 (Table 1). The modified method can be successfully applied to an α-amino acid derivative
研究了1 H-吲哚-4-丙酸衍生物的Vilsmeier-Haack型环化作为麦角酸A–B–C环系统的模型构建(1)。在MeCN中存在K 2 CO 3的情况下,通过Vilsmeier-Haack反应可实现从1 H-吲哚的4位到3位的平稳环化,发现最佳的底物是N,N-二甲基羧酰胺9(表1)。修改后的方法可成功地应用到α -氨基酸衍生物与受保护的Ñ -乙酰基函数,即,至27(表2);然而,当使用手性底物(S)-27时,在环化中观察到光学纯度的损失(方案5)。另一方面,相应的亚砜20的分子内Pummerer反应提供了含S的三环体系22,其通过环化至5位而形成(方案3)。