A rhodanine derivative and its cycloadduct with diphenyl nitrile imine

The phenylmethylene substituent at the C5 position of 5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one, CI6HIINOS2, (I), is virtually coplanar with the planar five-membered ring, whereas the phenyl group at N3 is almost orthogonal to this plane. The crystals of the chiral cycloadduct, 7-benzylidene-2,4,9-triphenyl-1,6-dithia-3,4,9-triazaspiro[4.4]non-2-en-8-one, C29H21N3OS2, (III), are racemic. Both five-membered rings have an envelope conformation with the spiro-C atom as the envelope flap, although this envelope is quite flattened for the 1,3-thiazolidine ring. In both compounds, short intramolecular C-H...S contacts cause visible steric strain. The known starting material, (I), has been prepared by condensation of 3-phenyl-2-thioxothiazolidin-4-one and benzaldehyde. Its reaction with N-phenylbenzohydrazonoyl chloride, (II), in the presence of triethylamine yielded (III) via 1,3-dipolar cycloaddition of the intermediate nitrile imine.