Two thiazolino[2,3-a]isoquinolinone S-oxides

The structures of two racemic thiazolino[2,3-a]isoquinolinone S-oxides, i.e. 8,9-dimethoxy-2,3,5,6-tetrahydro-10bH-thiazolo[2,3-a]isoquinolin-3-one 1-oxide [C13H15NO4S, (IIa)] and 8,9-dimethoxy-10b-methyl-2,3,5,6-tetrahydro-10bH-thiazolo[2,3-a]isoquinolin-3-one 1-oxide [C14H17NO4S, (IIb)], are described. The thiazolinone ring in (IIa) exists in an envelope conformation, while in (IIb), it assumes a half-chair conformation. In (IIa) and (IIb), the six-membered heterocyclic ring adopts an envelope conformation. The O atom at sulfur is oriented in a pseudo-axial position, whereas the H atom in (IIa) and the methyl group in (IIb), linked to the stereogenic C centre, occupy a bisectional position with respect to the partially saturated pyridine ring and a pseudo-axial position with respect to the thiazolinone ring. In both structures, the S=O group and the substituent at the stereogenic C centre are trans with respect to one another. Intermolecular C-H...O hydrogen bonds are observed in the crystal lattice of (IIa) and (IIb).