4-Hydroxycoumarin reacts with α,β-unsaturated iminium salts derived from enals to give 1,2-addition products, exclusively. The resulting adducts further react intramolecularly, affording substituted 2H-pyrrano[3,2-c]coumarins in good yields. α,β-Unsaturated iminium salts derived from enones afford substituted 3,4-dihydro-2-hydroxy-2H,5H-pyrano[3,2-c]coumarins by intramolecular cyclisation of the Michael adduct.
4-羟基
香豆素与来自烯醛的α,β-不饱和
亚胺盐反应,生成1,2-加成产物,且仅此类产品。由此生成的加合物进一步发生分子内反应,生成取代的
2H-吡喃[3,2-c]
香豆素,产率良好。来自酮的α,β-不饱和
亚胺盐通过迈克尔加合物的分子内环化反应生成取代的3,4-二氢-2-羟基-2H,5H-
吡喃[3,2-c]
香豆素。