Intermolecular [3+2] Annulation of Cyclopropylanilines with Alkynes, Enynes, and Diynes via Visible Light Photocatalysis

Abstract

One-step synthesis of carbocycles substituted with amines from simple starting materials remains rare. We recently developed intermolecular [3+2] annulation of cyclopropylanilines with alkenes and alkynes that enable this one-step synthesis. Herein, we report our findings for a fullscale study of the annulation. Significant expansion of the substrate scope for both cyclopropylanilines and alkynes is achieved. A range of structurally diverse carbocycles substituted with amines is prepared.

Dirhodium(II)-catalyzed [3 + 2] cycloaddition of N-arylaminocyclopropane with alkyne derivatives

“…For 2-methylbut-1-en-3-yne ( 2i ) containing both terminal alkenes and alkynes, the activity of the olefin was greater than that of the alkyne, which favors alkene cycloaddition products with a ratio of 89:11. The observed selectivity of product 4i is similar to that previously reported [11] (Table 3, entry 8), indicating the results of this type of reaction are mainly determined by the stability of the free radical intermediate during the reaction. Further investigation revealed cycloaddition preferentially proceeded with the terminal alkene or alkyne.…”

The Cleavage of a CC Bond in Cyclobutylanilines by Visible‐Light Photoredox Catalysis: Development of a [4+2] Annulation Method

“…A catalytic cycle similar to the [3+2] annulation is proposed for the [4+2] annulation (see SI) 3b,c. The oxidation peak potential of 1 a was found to be 0.8 V versus SCE, which is more positive than the reduction potential of the photoexcited 4 a (Ir 3+ */Ir 2+ : 0.66 V vs. SCE).…”

“…Internal alkynes were unsuccessful in the annulation with cyclopropylanilines 3b. c Surprisingly, divergent reactivity emerged between cyclopropylanilines and cyclobutylanilines with respect to this class of alkynes. Several internal alkynes ( 2 f – h ) successfully underwent the annulation reaction with cyclobutylanilines under complete regiocontrol.…”

Visible‐Light‐Mediated Ring‐Opening Reactions of Cyclopropanes

“…In the same year, Zheng group further extended the scope of this [3 + 2]-cycloaddition of cyclopropylanilines 62/71 by reacting them with a wide variety of alkynes 13 a/64/65/68 (Scheme 46). [90] Symmetrical and asymmetric diynes 64/65 were used in the reaction, and the products 66/67 were formed in moderate to good yields with excellent regio-and diastereoselectivities. When eneynes 68 were employed for the reaction, the products 69/70 were isolated in good yields with poor regioselectivity.…”

“…Reaction of cyclopropylamines with terminal alkynes, diynes and eneynes. [90] Scheme 47. Reaction of cyclopropylamines with cyclopropenes.…”