Hypervalent S-Cl bond in cyclic acylaminochloro-lambda(4)-sulfanes: a comparison of N-S-Cl, N-S+ClO4- and N-S+center dot center dot center dot O=C bond systems

Two cyclic acylaminochloro-lambda(4)-sulfanes containing a five- or a six-m embered hetero ring (5 and 6), as well as their cyclic acylaminosulfonium s alt 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 diffr action. Compounds 5, 6, 9 and 10 exhibit a trigonal bipyramidal configurati on about the central sulfur atom, with nitrogen and chlorine (in 5 and 6) o r with nitrogen and oxygen atoms (in 9 and 10) in axial positions. In sulfo nium salts 7 and 8, the bond angles about sulfur an similar to those obtain ed for analogous lambda(4)-sulfanes 5 and 6. The interatomic S-N distances, which range from 1.66 to 1.73 Angstrom, point to a strong covalent bond in an compounds investigated. In lambda(4)-sulfanes the axial S-Cl hypervalen t bond (2.69 Angstrom in 5, 3.10 Angstrom in 6) is rather long and markedly polarized. In methoxycarbonyl-substituted acylaminosulfonium salts the int eratomic S ... O distances are 2.41 Angstrom (in 9) and 2.74 Angstrom (in 1 0). The individual S-N, S-Cl, S ... O and S-C-ar bond lengths, as well as t he 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 degrees, 90-104 degrees, 85-96 degr ees and 101-104 degrees, respectively), which depend on both the axial subs tituents on sulfur and the size of the hetero ring, are compared and discus sed. The five-membered 2,3-dihydro-isothiazole rings in 5, 7 and 9 are prac tically planar, whereas the 1,2-oxathiole "ring" in 10 is unusually puckere d. The six-membered dihydro-1,2-thiazine rings in 6, 8 and 10, as well as t he 1,2-oxathiine "ring" in 9, assume a more or less inverted half-chair for m. The orientations of the aromatic rings in relation to the C-ar(eq)-S-C-a r'(eq) plane are also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.