Intramolecular Dearomatizing [3 + 2] Annulation of α-Imino Carbenoids with Aryl Rings Furnishing 3,4-Fused Indole Skeletons

Abstract

The rhodium-catalyzed dearomatizing [3 + 2] annulation reaction of 4-(3-arylpropyl)-1,2,3-triazoles is described. It provides a straightforward synthetic pathway from simple 5-aryl-1-alkynes leading to tricyclic 3,4-fused dihydroindoles via the corresponding 1,2,3-triazoles.

Synthetic Methods for 3,4‐Fused Tricyclic Indoles via Indole Ring Formation

“…In 2014, Miura and Murakami et al. established an innovative synthetic strategy for 3,4‐fused tricyclic indole structures from readily available arenes with an N ‐sulfonyl‐1,2,3‐triazole unit acting as the precursor of α‐imino rhodium carbenoid (Scheme ) . When compound 57 was treated with 1 mol% of Rh 2 (OCO t‐ Bu) 4 , electrophilic rhodium carbenoid species 61 was generated and reacted with the phenyl group in a 6‐exo mode, providing zwitterionic intermediate 62 .…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…1046) in a process involving copper-catalyzed 1,3-dipolar cycloaddition, rhodium catalyzed formation of an α-iminocarbene complex (e.g. 1045), and cycloaddition [1114]. A related triple catalyst system (copper, rhodium, and gold) was employed for the synthesis of dihydropyrroles (e.g.…”

Efficient synthesis of indoles from 2-alkynylaniline derivatives in water using a recyclable copper catalyst system

“…22 However, many problems, especially those related to the tolerance of the functional group towards alkaline conditions, remained unresolved until the pilot work employing Cu(II) catalysts reported by Hiroya et al 22 in 2004, in which either sulfonamides or unsubstituted primary and secondary aniline derivatives could be cyclized into corresponding indoles. Henceforth, copper 18,22,[40][41][42][43][44][46][47][48]53,54 and many other inexpensive catalysts (metal or nonmetal, such as Hg [55][56][57] , Zn 58-61 and I 62 ) have received much attention for use in functionalized indole synthesis, although noble metals are necessary for some special purposes. 14,28,30,34,63 Water is the most environmentally benign and inexpensive medium, and its use often leads to the observation of unique reactivity and a simplified separation process.…”