Dual roles of bisphosphines and epoxides: Rh-catalyzed highly chemoselective and diastereoselective (3 + 2) transannulations of 1, 2, 3-thiadiazoles with cyanoepoxides. Issue 23 (27th October 2021)

• Record Type: Journal Article
• Authors: Dong, Ziyang; Chen, Cunzhi; Wang, Jing; Xu, Jiaxi; Yang, Zhanhui
• Is Part Of: Organic chemistry frontiers. Volume 8:Issue 23(2021)
• Page Start: 6687
• Page End: 6698
• Publication Date: 2021-10-27
• Subjects: Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1039/d1qo01220g
• Languages: English
• ISSNs: 2052-4110

Abstract

Abstract : Dual roles of bisphosphines and epoxides are demonstrated in highly chemoselective and diastereoselective (3 + 2) transannulations. Abstract : A highly diastereoselective and chemoselective (3 + 2) transannulation of 1, 2, 3-thiadiazoles with cyanoepoxides has been discovered. The use of sterically larger DPEPhos allows the preparation of cis -epoxyl isothiazoles from cis -cyanoepoxides in up to 95% yields and 100 : 0 dr, while the use of sterically smaller DPPF allows the synthesis of trans -products from cis - or trans -cyanoepoxides in up to 95% yields and 100 : 0 dr. Bisphosphines and epoxides play dual roles. Bisphosphines serve not only as ligands, but also as catalysts to catalyze the isomerization of cis -epoxides to trans -isomers. The diastereoselectivity is controlled by the kinetic competition between the direct transannulation of cis -cyanoepoxides and the bisphosphine-catalyzed isomerization of cis -products. The epoxy group's large steric hindrance guarantees excellent chemoselectivity toward the (3 + 2) annulation, and its electron-withdrawing ability significantly improves the reactivity of the adjacent cyano group. To address the controversy over the organorhodium intermediates, we suggest the resonation between Lee's umpolung 1, 3-dipoles, Bao's cyclometalated Rh(iii ) complexes, and our thioacyl-coordinated Rh(i ) carbenes. Stereospecific access to isothiazole-fused γ-lactone is also developed.