Phosphine-catalyzed [5+1] annulation of δ-sulfonamido-substituted enones withN-sulfonylimines: a facile synthesis of tetrahydropyridines

Abstract

The first phosphine-catalyzed [5+1] annulation of enones with N-sulfonylimines works efficiently to give tetrahydropyridines.

Unexpected ring-opening of 2,3-dihydropyridines

“…Due to this positional change of the double bond we observed the following shifts of signals in 13 C NMR spectra of 9b compared to the hydrochlorides 6c, 7b, and 7c: the signals of C-3 and C-5 were shifted 3-4 ppm downfield, whereas, the resonance of C-1 shifted 17 ppm to lower frequencies. Furthermore, we observed a separation of the NCH 2 signals in 1 H NMR spectra due to the loss of rotatability caused by the formed double bond (Fig. 2).…”

“…Some spectra were acquired in DMSO-d 6 . In this case the central peaks of the DMSO-d 5 signal at 2.49 ppm in 1 H spectra and at 39.7 ppm in 13 C spectra served as internal reference. Abbreviations: aromatic H, ArH; aromatic C, ArC, quaternary aromatic C, ArC q .…”

“…Coupling constants (J) are reported in Hertz (Hz). 1 H and 13 C resonances were assigned using 1 H, 1 H-and 1 H, 13 C-correlation spectra.…”

“…R f = 0.78 (CH 2 Cl 2 :MeOH = 9:1); m.p. : 118 °C (EtOH); 1 Ethyl acetate was added with stirring and the solid was sucked off, washed with ethyl acetate, and purified using CC with (CH 2 Cl 2 :MeOH = 9:1) as eluent giving a yellow solid. Yield: 262 mg (21%) of 7c.…”

“…Sulfonylimines have been described recently as important reagents and intermediates for the syntheses of heterocycles [1][2][3], heterocyclic arrangements [4], cycloadditions [5,6] and asymmetric Friedel-Crafts reactions [7] as well as for the synthesis of natural products [8,9]. They were investigated for their antimicrobial [10,11], herbicidal [12,13], and anticancer [14] activities.…”