Diaryldiacyloxyspirosulfuranes. Part 3. Sulfuranes with five-, six- and seven-membered spirorings: syntheses and molecular structures

Abstract

Three novel diaryldiacyloxyspirosulfuranes (2–4) with five-, six- and seven-membered spirorings have been prepared, and their molecular structures determined by X-ray diffraction. The structure of spirosulfurane 1 with two identical five-membered spirorings has been reinvestigated. In all spirosulfuranes 1–4 the arrangement of the ligands about the central sulfur atom show a slightly distorted trigonal bipyramidal (TBP) geometry resulting in chiral molecular structure. The axial (hypervalent) S–O and equatorial (covalent) S–C_ar bond lengths range from 1.838(1) to 1.872(3) and from 1.771 (3) to 1.794(4)Å, respectively. The axial O–S–O and equatorial C_ar–S–C_ar bond angles lie in the narrow intervals of 174.9(2)–177.4(4)° and 105.8(2)–106.9(2)°, respectively. The five-membered spirorings are practically planar in 1–3. The six-membered spirorings in 2 and 4 assume distorted sofa conformations. The seven-membered spiroring in 3, having four C_ar atoms with planar configuration, is irregular. The aromatic rings fused with the spirorings are perpendicular to the equatorial plane only if the spiroring is five-membered. In other cases the stable conformations with TBP geometry about sulfur involve a significant torsion of the aromatic ring about the S–C_ar axis. Thus, in diaryldiacyloxyspirosulfuranes having acyloxy-O ligands at axial positions the structural parameters about the sulfur are not considerably influenced by the shape and size of the spirorings. The O–S–O moiety with hypervalent bonds may be regarded as a structural unity. The sum of the individual S–O bond lengths, (3.684–3.744 Å) which is characteristic of diaryldiacyloxyspirosulfuranes, differs markedly from the values found earlier for dialkoxy- and acyloxy-alkyloxy analogues (3.601 and 3.910 Å, respectively). For spirosulfurane 3 a rearrangement into the isomeric ten-membered cyclic anhydride 13 is observed.