Rhodium-Catalyzed One-pot Chemoselective Insertion-Rearrangement-Cyclization of Azavinyl Carbenes with 2-Aminobenzyl Alcohols.

Chemoselective insertion of in situ generated α-imino rhodium carbene onto the O-H bond of 2-aminobenzyl alcohols over the N-H bond followed by [1,3]-alky shift has been successfully accomplished for the synthesis of amine tethered ketone derivatives. The resultant product was further cyclized under acidic conditions to afford biologically important 3-aminoquinolines. Successful integration of chemoselective insertion-cum-rearrangement and cyclization in one pot offered access to various 3-aminoquinolines in a good yield. Conversion of 3-aminoquinolines into biological important motifs has also been demonstrated.

1,2,3-Triazole and Its Analogues: New Surrogates for Diazo Compounds.

Readily accessible and shelf-stable 1,2,3-triazole and its analogues such as pyridotriazole, triazoloindole, benzotriazole, and thiadiazole exist in equilibrium with their ring-opened isomers, viz., diazo compounds. These ring-opened isomers could be trapped by various metal catalysts (e.g., Rh, Pd, Cu, Co, Ag, etc.) to generate the corresponding metal carbenoids with extrusion of nitrogen. As a consequence, these unique N-heterocycles facilitate access to a realm of N-containing complex structural motifs of biological importance through denitrogenative transformations such as transannulations, insertions, ylide formation, and rearrangements by trapping of the metal carbenoids with a diverse range of coupling partners (e.g., alkenes, alkynes, nitriles, carbo/heterocycles, X-H/C-X bonds, etc.). Hence, suitably substituted triazole derivatives have emerged as efficient surrogates of diazo compounds for the generation of reactive metal carbenoids during the past decades. In this comprehensive review, we aim to discuss in detail the remarkable advancement in their synthesis and synthetic applications.

Rhodium-Catalyzed [4 + 2]-Annulation of o-Acylanilines with N-Sulfonyl-1,2,3-triazoles: Synthesis of 3-Aminoquinolines.

Efficient synthesis of 3-aminoquinolines has been demonstrated from readily accessible N-sulfonyl-1,2,3-triazoles and o-acylaniline derivatives. This transformation involves the generation of C-C and C-N bonds through insertion of rhodium azavinyl carbenoid into a N-H bond followed by cyclization and aromatization. The important features include good functional group tolerance, synthesis of indoloquinoline, and isolation of N-H-inserted product, a potential intermediate.

Rhodium Catalyzed [4 + 1]-Annulation of o-Acylanilines with 3-Diazoindoline-2-imines.

An efficient rhodium catalyzed [4 + 1]-annulation of o-acylanilines with 3-diazoindoline-2-imines has been successfully accomplished for the synthesis of spiroindolines in good to excellent yield. The reaction occurs through formation of N-ylide followed by cyclization and showed good tolerance to various functional groups. Gram-scale synthesis, diastereoselective construction of tetrasubstituted indoline, synthesis of spirooxindole, and isolation of potential intermediates have also been demonstrated.

Synthesis of Dihydro-3,1-benzoxazine Derivatives from 1,3-Amino Alcohols and N-Sulfonyl-1,2,3-triazole.

An efficient rhodium-catalyzed synthesis of dihydro-3,1-benzoxazine derivatives has been accomplished from aniline-derived 1,3-amino alcohols and N-sulfonyl-1,2,3-triazole. The developed reaction demonstrates the new reactivity of azavinyl carbenes and allows access to diverse substituted dihydro-3,1-benzoxazines in good yields. Importantly, the reaction was readily extended to diols and could be used for selective protection of amino alcohols with N-sulfonyl-1,2,3-triazole as the protecting reagent.