Enantioselective Dearomative [3+2] Cycloaddition Reactions of Benzothiazoles

Abstract

A highly enantioselective dearomative [3+2] cycloaddition of benzothiazole has been successfully developed. A wide range of benzothiazoles and cyclopropane-1,1-dicarboxylates are suitable substrates for this reaction. The desired hydropyrrolo[2,1-b]thiazole compounds were obtained in excellent enantioselectivity and yields (up to 97 % ee and 97 % yield). With the same catalytic system, a highly efficient kinetic resolution of 2-substituted cyclopropane-1,1-dicarboxylates was also realized.

Asymmetric Catalytic Reactions of Donor–Acceptor Cyclopropanes

“…In the case of benzothiazole dipolarophiles, the aromaticity of the nitrogen‐containing heterocycles was lost to form fused‐ring systems. Guo and You developed a chiral L7 /MgI 2 complex that catalyzed dearomative [3+2] cycloaddition with benzothiazoles to yield hydropyrrolo[2,1‐ b ]thiazole 15 in excellent enantioselectivity and yield [19] . Interestingly, unlike Johnson's work, [18] this reaction underwent a simple kinetic resolution process for both electron‐rich and ‐poor aryl‐substituted cyclopropanes.…”

“…In the case of benzothiazole dipolarophiles,t he aromaticity of the nitrogen-containing heterocycles was lost to form fused-ring systems.Guo and Youdeveloped achiral L7/MgI 2 complex that catalyzed dearomative [3+ +2] cycloaddition with benzothiazoles to yield hydropyrrolo[2,1-b]thiazole 15 in excellent enantioselectivity and yield. [19] Interestingly,u nlike Johnsonsw ork, [18] this reaction underwent as imple kinetic resolution process for both electron-rich and -poor arylsubstituted cyclopropanes.T he construction of aq uaternary stereogenic center using the bulkier 2-methyl benzothiazole as the dipolarophile failed due to the low reactivity of 2-aryl cyclopropanes (Scheme 9a). Very recently,t hey used more reactive aminocyclopropane 10 as the substrate to realize the asymmetric [3+ +2] cycloaddition with 2-substituted benzothiazoles.S imilarly,w ith the L5/Cu(OTf) 2 complex, the enantioselectivity of the products 17 and the recovered 10 changed following opposite trends as the reaction proceeded.…”

Co(III)/Zn(II)-catalyzed dearomatization of indoles and coupling with carbenes from ene-yne ketones via intramolecular cyclopropanation

“…A hexacyclic ring system that includes a unique cyclopropyl ring fused to an indoline accompanied by three quaternary carbon stereocenters such as lundurines are attractive targets. Traditional methods to construct cyclopropane-fused indoline derivatives include transition-metal-mediated reactions [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36], the classic Simmons-Smith reaction and so on [34][35][36][37][38][39][40][41]. However, highly efficient, environmentally friendly, and atom-economic methods for generating available carbenoids precursors in a catalytic fashion continue to be highly limited [42].…”

Ring Opening of Donor–Acceptor Cyclopropanes with N-Nucleo­philes

“…However, usually it is impossible to isolate the corresponding intermediates that readily form the resulting heterocycles. These reactions, which have been reported in a large series of papers [formal (3+2)-cycloadditions to imines, [32][33][34][35] diazenes, [36][37][38][39] N-aryls, [40][41][42] heterocumulenes, [43][44][45] nitriles, [46][47][48][49][50][51][52][53] as well as (3+3)-cycloadditions [54][55][56][57] ], form an independent branch in DA cyclopropane chemistry that is considered to be beyond the scope of this review.…”