Cu(II)-Catalyzed [3+2] Annulation of Thioamides with AIBN: Facile Access to Highly Functionalized Thiazolidine-4-ones

An efficient and versatile copper-catalyzed unprecedented intermolecular radical [3 + 2] annulation of thioamides with azobisisobutyronitrile (AIBN) is described. This two-component one-pot copper(II)-catalyzed transformation has been achieved via cascade formation of C-S/C−N bonds through the cyclization of in situ generated N,S-acetal intermediate from β-ketothioamide. This operationally simple method allows direct access to synthetically demanding thiazolidin-4-ones in good to excellent yields containing diverse functional groups of different electronic and steric nature. Remarkably, the readily available reaction partners, avoidance of expensive/toxic reagents and the gram scale synthesis are additional attributes to this strategy. AIBN here plays a dual role as radical initiator and unusual source of two carbon coupling partner. Notably, the products possess Z-stereochemistry with regard to the exocyclic C=C double bond at the 2-position of the thiazolidine ring.

Crystal structure and Hirshfeld surface analysis of (E)-3-[(4-methylbenzylidene)amino]-5-phenylthiazolidin-2-iminium bromide N,N-dimethylformamide monosolvate

In the cation of the title salt, C17H18N3S+·Br−·C3H7NO, the central thiazolidine ring adopts an envelope conformation with puckering parameters Q(2) = 0.310 (3) Å and φ(2) = 42.2 (6)°. In the crystal, each cation is connected to two anions by N—H... Br hydrogen bonds, forming an R 4 2(8) motif parallel to the (10\overline{1}) plane. van der Waals interactions between the cations, anions and N,N-dimethylformamide molecules further stabilize the crystal structure in three dimensions. The most important contributions to the surface contacts are from H...H (55.6%), C...H/H...C (17.9%) and Br...H/H...Br (7.0%) interactions, as concluded from a Hirshfeld analysis.

Crystal structure and Hirshfeld surface analysis of (E)-3-(benzylideneamino)-5-phenylthiazolidin-2-iminium bromide

The central thiazolidine ring of the title salt, C16H16N3S+·Br−, adopts an envelope conformation, with the C atom bearing the phenyl ring as the flap atom. In the crystal, the cations and anions are linked by N—H...Br hydrogen bonds, forming chains parallel to the b-axis direction. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H...H (46.4%), C...H/H...C (18.6%) and H...Br/Br...H (17.5%) interactions.

(3S,5R,6S)-Diphenylmethyl 1-oxo-6-bromopenicillanate

In the title compound, C21H20BrNO4S, a key intermediate in the synthesis of the widely used β-lactamase inhibitor tazobactam, the five-membered thiazolidine ring adopts an envelope conformation and the four-membered azetidine ring is in a distorted planar conformation. The crystal structure features C—H...O hydrogen bonds and a weak C—H...π interaction.

Crystal structure and Hirshfeld surface analysis of 3-amino-5-phenylthiazolidin-2-iminium bromide

In the cation of the title salt, C9H12N3S+·Br−, the thiazolidine ring adopts an envelope conformation with the C atom adjacent to the phenyl ring as the flap. In the crystal, N—H...Br hydrogen bonds link the components into a three-dimensional network. Weak π–π stacking interactions between the phenyl rings of adjacent cations also contribute to the molecular packing. A Hirshfeld surface analysis was conducted to quantify the contributions of the different intermolecular interactions and contacts.

Crystal structure and Hirshfeld surface analysis of (E)-3-[(4-chlorobenzylidene)amino]-5-phenylthiazolidin-2-iminium bromide

The title salt, C16H15ClN3S+·Br−, is isotypic with (E)-3-[(4-fluorobenzylidene)amino]-5-phenylthiazolidin-2-iminium bromide [Khalilov et al. (2019). Acta Cryst. E75, 662–666]. In the cation of the title salt, the atoms of the phenyl ring attached to the central thiazolidine ring and the atom joining the thiazolidine ring to the benzene ring are disordered over two sets of sites with occupancies of 0.570 (3) and 0.430 (3). The major and minor components of the disordered thiazolidine ring adopt slightly distorted envelope conformations, with the C atom bearing the phenyl ring as the flap atom. In the crystal, centrosymmetrically related cations and anions are linked into dimeric units via N—H...Br hydrogen bonds, which are further connected by weak C—H...Br contacts into chains parallel to the a axis. Furthermore, not existing in the earlier report of (E)-3-[(4-fluorobenzylidene)amino]-5-phenylthiazolidin-2-iminium bromide, C—H...π interactions and π–π stacking interactions [centroid-to-centroid distance = 3.897 (2) Å] between the major components of the disordered phenyl ring contribute to the stabilization of the molecular packing. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions for the crystal packing are from H...H (30.5%), Br...H/H...Br (21.2%), C...H/H...C (19.2%), Cl...H/H...Cl (13.0%) and S...H/H...S (5.0%) interactions.

Crystal structure and Hirshfeld surface analysis of (E)-3-[(4-fluorobenzylidene)amino]-5-phenylthiazolidin-2-iminium bromide

In the cation of the title salt, C16H15FN3S+·Br−, the phenyl ring is disordered over two sets of sites with a refined occupancy ratio of 0.503 (4):0.497 (4). The mean plane of the thiazolidine ring makes dihedral angles of 13.51 (14), 48.6 (3) and 76.5 (3)° with the fluorophenyl ring and the major- and minor-disorder components of the phenyl ring, respectively. The central thiazolidine ring adopts an envelope conformation. In the crystal, centrosymmetrically related cations and anions are linked into dimeric units via N—H...Br hydrogen bonds, which are further connected by weak C—H...Br hydrogen bonds into chains parallel to [110]. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H...H (44.3%), Br...H/H...Br (16.8%), C...H/H...C (13.9%), F...H/H...F (10.3%) and S...H/H...S (3.8%) interactions.