Borane-catalyzed dehydrogenative C–C bond formation of indoles with N-tosylhydrazones: an experimental and computational study

Abstract

A novel dehydrogenative C‒C bond formation of indoles and N-tosylhydrazones to di(indolyl)methanes (DIMs) has been demonstrated using tris(pentafluorophenyl)borane as catalyst. A wide range of functional groups can be tolerated under...

Cu(II)-Catalyzed Aminocyclization of N-Propargyl Hydrazones to Substituted Pyrazolines

“…Having this information in hand, the electronic effect of the substituents present in the aryl ring attached to the imine carbon of N -tosyl hydrazone was examined by the Hammett study (Scheme e). The reaction of 1 to afford 2c gave a negative ρ value of −1.14 after Hammett analysis, suggesting substantial cationic character on the transition state during the rate-determining step of the reaction, which is probably the cyclization step. , Finally, a control experiment with water confirmed the involvement of moisture in the formation of pyrazoline 2c , which was not observed under moisture-free conditions (Scheme f). This above information plausibly suggests that the overall reaction rate might be involved in two steps: (i) the rate of cyclization, which is probably the consumption rate of the starting material, and (ii) the rate of hydrolysis of the iminium ion, which is probably the formation of the final product.…”

B(3,4,5-F3H2C6)3Lewis acid-catalysed C3-allylation of indoles

“…6 The stereoselective C-glycosylation of indoles with B(C 6 F 5 ) 3 and glycosyl trichloroacetimidates has also been achieved by Mandal et al 7 The synthesis of bis(indolyl)alkanes by a B(C 6 F 5 ) 3 -catalysed Markovnikov addition of indoles to aryl alkynes as well as the B(C 6 F 5 ) 3 -catalysed dehydrogenative C-C bond formation of indoles with N-tosylhydrazones have also been reported. 8,9 An interesting new approach by Tang et al was the use of B(C 6 F 5 ) 3 as a single-electron oxidant. 10 Here, an electron donor-acceptor complex is formed between B(C 6 F 5 ) 3 and the indole which promotes a photoinduced single electron transfer event resulting in an oxidative C-S cross-coupling reaction of indoles with thiophenols.…”