Catalytic (3 + 2) umpolung annulations of α-thioacyl carbenes with aryl isothiocyanates

Abstract

1,2,3-Thiadiazoles serve as masked S-electrophilic thia-1,3-dipoles. Under rhodium/racemic BINAP catalysis they undergo denitrogenative (3 + 2) umpolung transannulations with aryl isothiocyanates with inverse regioselectivity and excellent stereoselectivity, yielding N-aryl 3H-1,2-dithiol-(Z)-3-imines...

The effect of the C5-substituent on regioselectivity in the Rh(i)-catalyzed intermolecular transannulation of 1,2,3-thiadiazoles with phenylacetylene

“…Transition metal-catalyzed denitrogenative transformations of 1,2,3-thiadiazoles have been demonstrated to be a facile and highly efficient approach to access structurally diverse heterocycles, [1][2][3] including thiophenes, [4][5][6][7][8] thiazoles, 9 isothiazoles, [10][11][12] 4H-thiopyran-4-ones, 13 thiochromenones, 14 1,3-thiaphospholes 15 and furans. 7,16 The mechanism of denitrogenative 1,2,3-thiadiazole transannulation reactions was investigated by Bao in 2021 using density functional theory (DFT) calculations, 17 with the structure of the key cyclometalated Rh(III) intermediate recently confirmed by our group using crystallographic data.…”

Isothiocyanates: happy-go-lucky reagents in organic synthesis

“…Yang group reported a Rh catalyzed [3 + 2] umpolung annulations of α-thioacyl carbenes derived from 1,2,3-thiadiazoles ( 77 ) with aryl isothiocyanates ( 78 ). 40 The reaction proceeded in umpolung, stereospecific, and regiospecific manner as more nucleophilic CS serves as the reactive site instead of the less nucleophilic CN bond of the isothiocyanate. On the other hand, 1,2,3-thiadiazoles act as masked S -electrophilic, thia-1,3-dipoles in this Rh-catalyzed redox-neutral [3 + 2] annulations.…”

Recent Advances in the Denitrogenative Annulation Reactions of 1,2,3‐Thiadiazoles

“…demonstrated that 1,2,3-thiadiazoles 132 can undergo denitrogenative transannulation with isothiocyanates 133 under Rh(I)/(�)-BINAP catalysis in the presence of CsI as an additive (Scheme 21a). [39] Similar to nitriles, in the presence of isothiocyanates, thiadiazoles 132 have been observed to exhibit inversed (umpolung-type) reactivity as masked S-electrophilic 1-thia-1,3-dipoles, affording 1,2-dithiapent-3-enes 134 exclusively, in a regiospecific and stereospecific fashion. Generally, the developed reaction has been demonstrated to have broad substrate scope and functional group compatibility, however, 1,2,3-thiadiazoles 135-140 were unsuccessful (Scheme 21b), and only aryl-substituted isothiocyanates were effective.…”