Mechanistic insights into the Rh(i)-catalyzed transannulation of 1,2,3-thiadiazoles with alkenes, alkynes, and nitriles: Does the intermediacy of α-thiavinyl Rh-carbenoids play an important role?

Abstract

Density functional theory (DFT) calculations were performed to gain an in-depth mechanistic understanding of the Rh(I)-catalyzed transannulation of 1,2,3-thiadiazoles with alkenes, alkynes, and nitriles. Computational results indicate that the denitrogenation...

Catalytic Diastereospecific and Enantioselective (3 + 2) Transannulations of 1,2,3-Thiadiazoles with Strained Norbornene Derivatives

“…Building on Bao’s theoretical calculations and Lee’s and our previous experiments, , we suggest a plausible mechanism for the (3 + 2) transannulation (Figure ). The decomposition of 1,2,3-thiadiazole 1 with phosphine-ligated iridium catalyst gives rise to a four-membered species that resonates between thioacyl Ir­(I) carbene A and cyclometalated Ir­(III) complex B (step a).…”

“…(For more failures, see Scheme S2 in the Supporting Information.) We assume that the added substituent(s) increases the steric hindrance of the CC plane and prevents its interaction with α-thioacyl rhodium carbene intermediates . To override this steric deactivation, we came up with a solution by using cyclic alkenes on the basis of the following two considerations: (1) The CC bond with Z-configuration shows smaller steric hindrance, especially for disubstituted alkenes.…”

“…The decomposition of 1,2,3-thiadiazole 1 with phosphine-ligated iridium catalyst gives rise to a four-membered species that resonates between thioacyl Ir­(I) carbene A and cyclometalated Ir­(III) complex B (step a). Bao and coworker’s calculation disclosed the planar stereogeometry of a cyclometalated Rh­(III) complex, which prompts us to propose a similar planarity for the iridium complex species B . The coordination of bicyclic alkene 2 from its sterically less exo side to the enantiotopic faces of B (Figure b, left or right approach) leads to complex C or ent - C depending on the chirality of the bisphosphine ligand used (step b).…”

Chemoselectivity in the Transannulaction of 1,2,3‐Thiadiazoles and Alk‐2‐enenitriles: Specific Synthesis of 3‐(Alk‐1‐enyl)isothiazoles

“…Based on the reported mechanism of the Rh (I)‐catalyzed (3+2) transannulation of 1,2,3‐thiadiazoles and the unsaturated bonds, [10,11] the plausible mechanism is proposed in Scheme 3. 1,2,3‐Thiadiazoles 1 and the rhodium catalyst first form four‐membered ring 1,2‐thiarhodocyclobut‐3‐ene intermediates A , equivalents of α‐thiocarbonyl rhodium carbenes, through α‐thiocarbonyl diazonium intermediates after loss of N 2 (path a).…”

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

“…Based on previous mechanistic studies, 5 c , d ,6,17 we put forward a tentative mechanism for the umpolung (3 + 2) transannulation (Scheme 4). Ligand exchange of [Rh(COD)Cl] 2 with (±)-BINAP followed by denitrogenative oxidative addition of 1,2,3-thiadiazoles 1 forms 1-thia-2-rhodacyclobutene species ( B ) (step a), which are suggested to resonate with thioacyl-coordinated Rh( i ) carbenes ( A ).…”