Rearrangement of Aryl- and Benzylthiopyridinium Imides with Participation of a Methyl Substituent

Abstract

6-Methyl substituted 2-aryl- and 2-benzylthiopyridinium N-imides reacted with an excess of isocyanates to give N,N-disubstituted exocyclic1H-imidazo[4,5-b]pyridin-2(3H)-ones. The products easily underwent spontaneous [1,5] hydrogen shift to provide the heteroaromatic imidazopyridinone isomers. The transformation implied the initial formation of [1,2,4]triazolo[2,3-a]pyridinium salt, followed by deprotonation and carbamoylation of the methylene moiety, and, finally, a rearrangement following a [1,3] sigmatropic pattern. Mechanistic considerations suggest and some experimental findings reveal the nonconcerted two-step mechanism of the ring transformation step.

Base-Mediated Hydroamination of Propargylamine: A Regioselective Intramolecular 5-exo-dig Cycloisomerization en Route to Imidazole-2-thione

“…Intramolecular reaction of 2-(2-alkynyl)anilines under the above conditions gave access to 2-substituted indoles . Imidazole-2-thione core is a key structural component of several bioactive molecules, and large numbers of synthetic approaches have been reported for the formation of this core . But synthesis of imidazole-2-thiones by hydroamination reaction of propargylamine remains an unexplored field.…”

Transformation of Zwitterionic Pyridine Derivatives to a Spiro-Fused Ring System: Azoniabenzo[de]fluorine. Synthesis and Mechanistic Rationalization

“…The NMR peak assignments were performed on the basis of one-( 1 H, 13 C NMR) and two-dimensional ( 1 H− 13 C-gHSQC, 1 H− 13 C-gHMBCAD) experiments. The coherence transfer delays in the 1 H− 13 C-gHSQC measurements were set to 1 / 4 J, where the one-bond J coupling was 140 Hz.…”

“…Recently we have found that arylsulfanopyridinium amidates ( 1 ) as reactive mesomeric betaines can serve as valuable starting materials for 1,3-dipolar cycloadditions and subsequent transformations. Thus, syntheses of triazolo­[2,3- a ]­pyridinium salts, pyrrolo­[3,2- b ]­pyiridines, imidazo­[4,5- b ]­pyridines, 4-azaindoles, , and 7-azaindoles have been elaborated.…”

“…;1 H NMR (400 MHz, DMSO) δ 3.24 (1H dd, J = 17.6, 11.7 Hz, H4 y ), 3.86 (1H, ddd, J = 11.7, 7.8, 6.4 Hz, H4a), 4.03 (1H, dd, J = 17.6, 7.8 Hz, H4 x ), 4.64 (1H, d, J = 10.2 Hz, H8), 6.09 (1H, dd, J = 10.2, 1.4 Hz, H7), 6.51 (1H, dd, J = 6.4, 1.4 Hz, H5), 6.83 (2H, m, H2″+ H6″), 7.28 (1H, d, J = 7.9 Hz, H1), 7.30−7.60 (8H, m, H2′ + H3′ + H4′ + H5′ + H6′ + H3″ + H4″ +H5″), 8.24 (1H, d, J = 8.1 Hz, H3), 8.55 (1H, dd, J = 8.1, 7.9 Hz, H2), 10.90 (1H, br. s, H9);13 C NMR (100 MHz, DMSO) δ 37.1 (C4), 45.3 (C4a), 61.2 (C11), 81.1 (C8a), 121.6 (C8), 123.5 (C3), 124.5 (C5), 125.3 (C7), 128.1 (C3″ + C4″ + C5″), 128.3 (C2′ + C6′), 128.7 (C1), 129.5 (C6), 130.0 (C3′ + C5′), 130.1 (C2″ + C6″), 136.2 (C1′), 141.6 (C1″), 146.2 (C2), 152.9 (C11a), 156.6 (C3a), 166.6 (C10).…”

Copper-Catalyzed Aerobic Oxidative [3+2] Annulation for the Synthesis of 5-Amino/Imino-Substituted 1,2,4-Thiadiazoles through C–N/N–S Bond Formation

“…2-Aminopyridine/amidine has long been realized as one of the most widely used commercial reagents in organic synthesis. In the past few decades, the 2-aminopyridines acted as a directing group providing a basic block for the elegant construction of five- or six-membered nitrogen-containing heterocyclic compounds by the formation of N–C, N–N, and N–O bonds . In 2013, our group also developed an efficient method for the synthesis of 2-haloimidazopyridines from aminopyridines and haloalkynes under a Cu/O 2 catalytic system, in which bidental nitrogen atoms of 2-aminopyridine might coordinate with Cu and then activate another substrate (Scheme ).…”