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-1 0bH-thiazolo- [2,3-a]isoquinolin-3-one 1-oxide [C14H17NO4S, (IIb)], are des cribed. The thiazolinone ring in (IIa) exists in an envelope conformation, while in (IIb), it assumes a half-chair conformation. In (IIa) and (IIb), t he six-membered heterocyclic ring adopts an envelope conformation. The O at om 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, oc cupy a bisectional position with respect to the partially saturated pyridin e ring and a pseudo-axial position with respect to the thiazolinone ring. I n both structures, the S=O group and the substituent at the stereogenic C c entre are trans with respect to one another. Intermolecular C-H . . .O hydr ogen bonds are observed in the crystal lattice of (IIa) and (IIb).