Hypervalent S–Cl bond in cyclic acylaminochloro-λ4-sulfanes: a comparison of N–S–Cl, N–S+ClO−4 and N–S+⋯OC bond systems

Abstract Two cyclic acylaminochloro-λ 4 -sulfanes containing a five- or a six-membered hetero ring ( 5 and 6 ), as well as their cyclic acylaminosulfonium salt analogues without ( 7 and 8 ) and with S⋯O close contact ( 9 and 10 ), have been prepared and their molecular structures determined by X-ray diffraction. Compounds 5 , 6 , 9 and 10 exhibit a trigonal bipyramidal configuration about the central sulfur atom, with nitrogen and chlorine (in 5 and 6 ) or with nitrogen and oxygen atoms (in 9 and 10 ) in axial positions. In sulfonium salts 7 and 8 , the bond angles about sulfur are similar to those obtained for analogous λ 4 -sulfanes 5 and 6 . The interatomic S–N distances, which range from 1.66 to 1.73 A, point to a strong covalent bond in all compounds investigated. In λ 4 -sulfanes the axial S–Cl hypervalent bond (2.69 A in 5 , 3.10 A in 6 ) is rather long and markedly polarized. In methoxycarbonyl-substituted acylaminosulfonium salts the interatomic S⋯O distances are 2.41 A (in 9 ) and 2.74 A (in 10 ). The individual S–N, S–Cl, S⋯O and S–C ar bond lengths, as well as the N(ax)–S–X(ax) (X=Cl or O), N(ax)–S–C ar (eq), Cl(ax)–S–C ar (eq) and C ar (eq)–S–C ar ′(eq) bond angles (159–176°, 90–104°, 85–96° and 101–104°, respectively), which depend on both the axial substituents on sulfur and the size of the hetero ring, are compared and discussed. The five-membered 2,3-dihydro-isothiazole rings in 5 , 7 and 9 are practically planar, whereas the 1,2-oxathiole “ring” in 10 is unusually puckered. The six-membered dihydro-1,2-thiazine rings in 6 , 8 and 10 , as well as the 1,2-oxathiine “ring” in 9 , assume a more or less inverted half-chair form. The orientations of the aromatic rings in relation to the C ar (eq)–S–C ar ′(eq) plane are also discussed.