From 4,5,6,7-tetrahydroindoles to 3- or 5-(4,5,6,7-tetrahydroindol-2-yl)isoxazoles in two steps: a regioselective switch between 3- and 5-isomers

Transition-Metal-Free Synthesis of Pyrrolo[1,2-a]pyrazines via Intramolecular Cyclization of N-Propargyl(pyrrolyl)enaminones

“…Versatile starting materials for the design of heterocyclic compounds, including condensed ones, are enaminones, due to the ambident electrophilicity of the enone and the nucleophilicity of the enamine moieties. 1 A variety of intramolecular reactions of enaminones leading to pyrrolines, 2 pyrroles, 3 indoles, 4 pyrazoles, 5 dihydropyridines, 6 pyridines, 3c pyrimidines, 7 and isoxazoles 8 have been implemented. Among the great diversity of enaminones, pyrrolylenaminones have, until now, remained insufficiently known, despite their great synthetic potential.…”

Recent Strides in the Transition Metal-Free Cross-Coupling of Haloacetylenes with Electron-Rich Heterocycles in Solid Media

“…Acylethynyltetrahydroindoles 71 readily cyclized with hydroxylamine to give regioselectively either 3-(4,5,6,7-tetrahydroindol-2-yl)-4,5-dihydroisoxazol-5-ols 72 or 5-(4,5,6,7-tetrahydroindol-2yl)isoxazoles 73 (Scheme 40) [82]. The cyclization can be easily switched from the direction leading exclusively to isoxazoles 72 to the formation of isoxazoles 73 by simple changing of the proton concentration in the reaction mixture.…”

“…Moreover, 4,5-dihydroisoxazol-5-ols 72 underwent easy aromatization when refluxing (benzene, 1 h) in the presence of TsOH•H 2 O to isoxazoles 74 in 73-91% yields (Scheme 42) [82].…”

GIAO‐DFT calculation of 15N NMR chemical shifts of Schiff bases: Accuracy factors and protonation effects

“…Many chemical transformations and rearrangements of diverse imines (in particular, oximes) utilized in the synthesis of azoles and larger nitrogen‐containing heterocycles (see classical paper by Trofimov and Mikhaleva together with some more recent contributions from this team) occur stereoselectively, which makes the problem of stereoelectronic effects at the C═N bond to be of crucial importance. In this connection, our earlier and later experimental and theoretical studies of imines received a new impact, especially in line with the recent breakthrough in the NMR‐oriented theory and computation including, in particular, general computational approaches for 15 N NMR chemical shifts …”