Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University, Hangzhou, 310027, Zhejiang (P. R. China), Fax: (+86) 21-6260-9305.
Chemistry. 2014 Nov 3;20(45):14589-93. doi: 10.1002/chem.201404769. Epub 2014 Sep 26.
[IPrAuCl]/AgSbF6 -catalyzed cyclization of the readily available 4-benzoxyl-1-(indol-2-yl)-2-alkynols occurred smoothly in 1,2-dichloroethane (DCE) in the presence of 4 Å MS to form a series of differently polysubstituted 2-oxygenated carbazole derivatives efficiently. Based on mechanistic study, a possible mechanism involving 1,3-migration of a benzoate group to form the allene, Au(+) -mediated cyclization-elimination to form a gold-carbene intermediate, and subsequent highly selective 1,2-migration has been proposed for the formation of carbazoles. Highly selective 1,2-migration referring to the two substituents R(3) and R(4) (R(4) =H, alkyl, and aryl group) was observed: (1) In the presence of both H and alkyl groups, 1,2-hydrogen migration is exclusive; (2) in the presence of a methyl group (R(3) ), propyl, isopropyl, 4-methylphenyl, and 4-chlorophenyl groups (R(4) ) migrate exclusively. Finally, the first total synthesis of the recently isolated naturally occurring carbazole alkaloid karapinchamine A in 5.2 g scale has been realized in 6 steps from commercially available chemicals without need for any protection-deprotection.
[IPrAuCl]/AgSbF6 催化的 4-苯甲酰基-1-(吲哚-2-基)-2-炔醇在 1,2-二氯乙烷（DCE）中在 4 Å MS 的存在下顺利环化，高效形成一系列不同多取代的 2-氧代咔唑衍生物。基于机理研究，提出了一种可能的机理，涉及苯甲酸酯基团的 1,3-迁移形成丙二烯，Au(+)介导的环化-消除形成金-碳烯中间体，以及随后高度选择性的 1,2-迁移形成咔唑。高度选择性的 1,2-迁移是指两个取代基 R(3)和 R(4)（R(4)=H、烷基和芳基）：（1）在 H 和烷基同时存在时，1,2-氢迁移是独占的；（2）在存在甲基（R(3)）时，丙基、异丙基、4-甲基苯基和 4-氯苯基（R(4)）是专一地迁移。最后，从商业可得的化学物质出发，在没有任何保护-脱保护的情况下，以 5.2 g 规模实现了最近分离的天然存在的咔唑生物碱卡兰品胺 A 的首次全合成，共 6 步。
