Sulfuranes with Oximate Axial Ligands

Article abstract of DOI:10.1021/jo00118a036

New sulfuranes having one or two axial oximate (R2C=NO) ligands were synthesized.An improved sulfurane-forming step, involving a rapidly stirred suspension of NaHCO3, is described.The failure of sulfide oximes in which sulfur bears one or two tertiary carbons to form sulfuranes is explained by a C-S bond cleavage leading to tertiary carbocations.This represents a hitherto unanticipated limitation to the standard method of sulfurane synthesis.The X-ray crystal structure of one of the new sulfuranes, namely 2,2'-spirobi(4-phenyl-3H-1,2,5-oxathiazoline), is reported (R = 0.0368).An unusual feature was the quite compressed equatorial (C-S-C) angle, 102.6(1) deg.The S-O bond length, 1.846(2) Angstroem, was similar to S-O bond lenghths of sulfuranes having two axial carboxylate ligands.Since the oximate ligand has not been used previously in a 10-S-4 species, an assessment of its apicophilicity relative to other more common axial ligands was made by considering X-ray structural data, IR data, and ab initio calculations.These suggest that the R2C=NO ligand is as apicophilic as the hexafluorocumyloxy (ArC(CF3)2O) ligand.