Convenient method for synthesis of thiazolo[3,2-a]pyrimidine derivatives in a one-pot procedure

Crystal structure of ethyl 2-acetyl-3,7-dimethyl-5-(thiophen-2-yl)-5H-thiazolo[3,2-a]pyrimidine-6-carboxylate

In the title compound, C₁₇H₁₈N₂O₃S₂, the pyrimidine ring adopts a shallow sofa conformation, with the C atom bearing the axially-oriented thio­phene ring as the flap [deviation = 0.439 (3) Å]. The plane of the thio­phene ring lies almost normal to the pyrimidine ring, making a dihedral angle of 79.36 (19)°. In the crystal, pairs of very weak C—H⋯O hydrogen bonds link the mol­ecules related by twofold rotation axes, forming R₂²(18) rings, which are in turn linked by another C—H⋯O inter­action, forming chains of rings along [010]. In addition, weak C—H⋯π(thio­phene) inter­actions link the chains into layers parallel to [001] and π–π inter­actions with a centroid–centroid distance of 3.772 (10) Å connect these layers into a three-dimensional network.

Crystal structure of ethyl 2-cyano-3-[(1-eth-oxy-ethyl-idene)amino]-5-(3-meth-oxy-phen-yl)-7-methyl-5H-1,3-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate

In the title compound, C22H24N4O4S, the central pyrimidine ring adopts a sofa conformation with the ring-junction N atom displaced by 0.2358 (6) Å from the mean plane of the remaining ring atoms. The 3-meth-oxy-phenyl ring, at the chiral C atom opposite the other N atom, is positioned axially and is inclined to the thia-zolo-pyrimidine ring with a dihedral angle of 83.88 (7)°. The thia-zole ring is essentially planar (r.m.s. deviation = 0.0034 Å). In the crystal, pairs of weak C-H⋯O hydrogen bonds link mol-ecules related by twofold rotation axes to form R 2 (2)(8) rings, which in turn are linked by weak C-H⋯N inter-actions, forming ribbons along [-110]. In addition, π-π stacking inter-actions [centroid-centroid distance = 3.5744 (15) Å] connect the ribbons, forming slabs lying parallel to (001).

The Eschenmoser coupling reaction under continuous-flow conditions

The Eschenmoser coupling is a useful carbon-carbon bond forming reaction which has been used in various different synthesis strategies. The reaction proceeds smoothly if S-alkylated ternary thioamides or thiolactames are used. In the case of S-alkylated secondary thioamides or thiolactames, the Eschenmoser coupling needs prolonged reaction times and elevated temperatures to deliver valuable yields. We have used a flow chemistry system to promote the Eschenmoser coupling under enhanced reaction conditions in order to convert the demanding precursors such as S-alkylated secondary thioamides and thiolactames in an efficient way. Under pressurized reaction conditions at about 220 °C, the desired Eschenmoser coupling products were obtained within 70 s residence time. The reaction kinetics was investigated and 15 examples of different building block combinations are given.