Reactions of PO(NCS)3 with 4-hydroxy-1,3-dioxanes. Crystal structure of rel-(2S,4R,5S,6S)-2,6-diethyl-5-methyl-4-(N'-benzylthioureido)-1,3-dioxane
Substituted 4-hydroxy-1,3-dioxanes II react rapidly with PO(NCS) 3 to give 4-isothiocyanato-1,3-dioxanes III . The 1 H NMR spectra showed that in the isothiocyanate IIIa the predominant stereoisomer has its NCS group in axial position. The addition of benzylamine to the isothiocyanates IIIa and IIIb gave uniform thioureas IVa and IVb with equatorial alkyl groups at 2 and 6 positions and axial thioureido group at 4 position. On the other hand, the isothiocyanate IIIc reacts with benzylamine to give a mixture of three stereoisomeric thioureas V,VI , and VIII . The structure of VI was proved by means of X-ray diffraction analysis; in crystalline form the molecules of VI are present as H-bonded dimers (N-H ... O).