Six-membered cyclic sulfites derived from glucofuranose and 1,2,4-butanetriol

Six-membered cyclic sulfites derived from glucofuranose derivatives 5, 6 and from 1-O-tert-butyldimethylsilil-1,2,4-butanetriol 12 were synthesized and separated into pure diastereomers which were in turn subjected to the sequence of reactions leading to the introduction of the terminal vinyl ether fragment. Reactivity and applicability of cyclic sulfites as intermediates in [2+2]cycloaddition of chlorosulfonyl isocyanate (CSI) to vinyl ethers were studied. The cycloaddition to vinyl ethers 19 and 20 proceeded in low yield and low asymmetric induction, in the case of the former, and moderate yield and pronounced asymmetric induction, in the case of the latter. The (1)H-NMR spectra of sulfites 13-16 reveal a preference of the sulfite oxygen atom for the axial position. Thus, well-defined conformation in solution for compounds 13 and 15 and a mixture of the two possible chair forms for sulfites 14 and 16 could be assigned. The stretching frequency of the S-->O bond in stable conformation with an axial sulfite oxygen occurs in the range 1,160-1,210 cm(-1), whereas conformationally mobile sulfites exhibit corresponding absorption above 1,220 cm(-1). The absolute configuration assignments of sulfites 7, 8, 15, 16 and 25-28 were done empirically based on the combined analysis of the NMR, IR, X-ray, and dichroic data. It was demonstrated that the sign of the Cotton effect around 194 nm correlated with the absolute stereochemistry at the sulfur atom in a sulfite chromophore.