DIARYLDIACYLOXYSPIROSULFURANES .3. SULFURANES WITH 5-MEMBERED, 6-MEMBERED AND 7-MEMBERED SPIRORINGS - SYNTHESES AND MOLECULAR-STRUCTURES

Three novel diaryldiacyloxyspirosulfuranes (2-4) with five-, six- and seven-membered spirorings have been prepared, and their molecular stru ctures determined by X-ray diffraction. The structure of spirosulfuran e 1 with two identical five-membered spirorings has been reinvestigate d. In all spirosulfuranes 1-4 the arrangement of the ligands about the central sulfur atom show a slightly distorted trigonal bipyramidal (T BP) geometry resulting in chiral molecular structure. The axial (hyper valent) 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) angstrom respectivel y. 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)-degrees and 105.8(2)-106.9(2)-d egrees, respectively. The five-membered spirorings are practically pla nar in 1-3. The six-membered spirorings in 2 and 4 assume distorted so fa conformations. The seven-membered spiroring in 3, having four C(ar) atoms with planar configuration, is irregular. The aromatic rings fus ed with the spirorings are perpendicular to the equatorial plane only if the spiroring is five-membered. In other cases the stable conformat ions with TBP geometry about sulfur involve a significant torsion of t he aromatic ring about the S-C(ar) axis. Thus, in diaryldiacyloxyspiro sulfuranes having acyloxy-O ligands at axial positions the structural parameters about the sulfur are not considerably influenced by the sha pe 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 angstrom) which is characteristic of diaryl diacyloxyspirosulfuranes, differs markedly from the values found earli er for dialkoxy- and acyloxy-alkyloxy analogues (3.601 and 3.910 angst rom, respectively). For spirosulfurane 3 a rearrangement into the isom eric ten-membered cyclic anhydride 13 is observed.