Rhodium-Catalyzed Denitrogenative Diazole–Triazole Coupling toward Aza-Bridged Structures and Imidazole-Based Chelating Ligands

Abstract

1,4,8-Triazaocta-1,3,5,7-tetraenes, generated in situ by Rh2(Piv)4-catalyzed denitrogenative coupling of pyrazoles with 1-sulfonyl-1,2,3-triazoles, smoothly form 2,6,8-triazabicyclo[3.2.1]­octa-3,6-dienes via intramolecular aza-Diels–Alder cycloaddition. This domino reaction, combined with the subsequent thermal or acid-catalyzed rearrangement of the cycloadducts, provides direct and flexible access to N-sulfonylated (Z)-2-(2-aminovinyl)­imidazoles.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Strelnikova and co‐workers, in 2021 reported an unprecedented Rh(II)‐catalyzed denitrogenative coupling reaction of 1,2,3‐triazoles 38 with pyrazoles 37 that proceeds via IMADA stepwise cycloaddition of the two‐atom‐linked azadiene‐azadienophile intermediates 1,4,8‐triazaocta‐1,3,5,7‐tetraenes A to form 2,6,8‐triazabicyclo[3.2.1]octa‐3,6‐dienes 39 (Scheme 11). [28] …”

Rhodium-Catalyzed Synthesis of 2-Aroylpyrimidines via Cascade Heteropolyene Rearrangement

“…Moreover, the ratios of compounds 7a and 8a were similar in both reaction mixtures, which provides one more piece of evidence that the reactions of triazole 2a with azirine 6 and isoxazole 1a proceed through the identical pathway. The structures of compounds 7a and 8a were assigned on the basis of the NMR spectra of the reaction mixture derived from isoxazole 1a (see Section 7 in the Supporting Information) and reported data. , Unfortunately, attempts to isolate the intermediates by column chromatography failed. Upon heating of the previously mentioned reaction mixtures for 25 min in toluene, the intermediates 7a and 8a were entirely transformed to pyrimidine 3a .…”

“…The reaction of 9 with 1a proceeds through ring opening of the isoxazole cycle to give 8-oxa-1,4-diazatetraene 10 . Several modes of cyclization for tetraene 10 are feasible: 1,6-cyclizations to 1,3-oxazine 7b and 1,2-dihydropyrazine 4d and an intramolecular aza-Diels–Alder (IMADA) reaction to bicyclic adduct 8b . The DFT calculations (wB97XD/cc-pvtz, polarizable continuum model (PCM) for toluene, 383 K) revealed that the formation of oxazine 7b (TS1) is the most low-barrier process (Figure ).…”