Synthesis Of Heterocycles Via Rhodium-catalyzed Reaction Of N-Sulfonyl-1,2,3-Triazoles

Metal carbene is widely used in organic synthesis. Metal-stabilized carbenes derived from diazo compounds have been widely reported in organic chemistry. Rhodium acetate(II) dimer catalyst can be used in place of copper catalyst to decompose diazo compounds. In early 21 st century, 1,2,3-triazoles gain more and more attention when the "Click" chemistry appears. In recent years, N-sulfonyl-1,2,3-triazoles, as one kind of diazo precursors, has been extensively studied. In the presence of metal catalyst, thermodynamical equilibrium between N-sulfonyl-1,2,3-triazoles and α-diazo imines can be broken to generate α-imino metallocarbenes. Since the electrophilicity of the metal carbene carbon and the nucleophilicity of the imine nitrogen atom, the active α-imino metallocarbenes intermediates can participate in a series of chemical reactions, which include C-H, O-H, N-H insertion, cyclopropanation, cycloaddition and ylide formation. New carbon-carbon bonds, carbon-hetero bond and cyclic compounds can be formed by these reactions. This paper mainly focuses on the research of Rh-catalyzed tandem reaction of N-Sulfonyl-1,2,3-triazoles and salicylaldehydes, and the synthesis of isoquinolines as well as its derivation research.(1) Rhodium-catalyzed synthesis of 2,5-epoxybenzo[f][1,4]oxazepines by tandem reaction of N-sulfonyl-1,2,3-triazoles and salicylaldehydes. Under a nitrogen atmosphere, the use of 1 mol% of Rh2(piv)4, N-sulfonyl-1,2,3-triazoles and salicyl aldehydes in toluene at 100 oC gave the best result. Most N-Sulfonyl-1,2,3-triazoles and salicyl aldehydes reacted smoothly to afford 2,5-epoxybenzo[f][1,4]oxazepines in moderate to high yield. The first mechanistic hypothesis involves O–H insertion, subsequent stepwise [3+2] cycloaddition and 1,2-shift of the proton, which leads to the formation of 2,5-epoxybenzo[f][1,4]oxazepines. The second mechanistic hypothesis is that oxazoline can be obtained by formal [3+2] cycloaddition, and it undergoes intramolecular hydroalkoxylation to afford 2,5-epoxybenzo[f][1,4]oxazepines.(2) Rhodium-catalyzed synthesis of 1,2-dihydroisoquinolines as well as its derivation research. Bromonium ylide is proposed as the key intermediate which can be formed from intramolecular nucleophilic attack of benzyl bromide to α-imino rhodium carbene. We tried one-pot cyclization/Suzuki-Miyaura cross coupling reaction and one-pot cyclization/Sonogashira cross coupling reaction. Most N-sulfonyl-1,2,3-triazoles reacted smoothly to afford the corresponding coupling products and a lot of functional groups were well tolerated in the reaction. 4-bromo-1,2-dihydroisoquinolines can be used in the synthesis of a variety of isoquinoline derivatives.