Thietane 1,1-dioxide

Whereas the transformations thietane - thietane oxide- thietane dioxide are easy to perform192, as is the reverse transformation thietane dioxides ->thietanes188, no method of reducing the sulfonyl group to a sulfoxy group is available as yet. 

The proton spectra analysis of thietane, thietane oxide and thietane dioxide at 100 and 300 MHz in the temperature range — 140 to 190 °C confirmed the puckered structure for the oxide (5a) with the sulfinyl oxygen in the equatorial orientation, as inferred from chemical-shift considerations180. It appears that the repulsive-type 1,3-interactions between the oxygen and the 3-substituents184 are operating between oxygen and the axial proton on C-3 in the unsubstituted thietane oxide (5a). For the thietane dioxide (5b ... 

The consequences with respect to the corresponding thietane dioxides are straightforward in the trans-isomer, 187a, one phenyl group (i.e. R1) is necessarily axial, whereas in the isomer 187b both substituents are equatorial (equation 76). Clearly these preferred conformations minimize the potential repulsive interaction between 1,3-diaxial substituents66. 

Similar calculations have been applied to the 3-substituted thietane dioxide series (i.e. 188(1 -3))198, assuming that only the constant C in the Karplus equation should be significantly affected by the substituents and by the oxidation state of sulfur. The results thus obtained were in poor agreement with X-ray data. 

The proton spectra of thietane oxide (5a) and thietane dioxide (5b) have been studied in order to evaluate whether the oxidation at the sulfur atom changes the established 35° puckering of the ring218, and whether a correlation is possible between structure and... 

It appears, however, that the most used strategy for the preparation of thietane dioxides is the [2 + 2] cycloaddition of enamines (202) with in situ-generated sulfenes (220)74,143,186 188,202,242 to give /(-aminothietane sulfones (equation 85). 

Although the yields of the above reactions are high and the procedure is simple186, there are some apparent disadvantages the selection of the sulfene substituents R1 and R2 is limited, depending on the availability of the sulfonyl chloride precursors the cycloaddition leads to a mixture of cis- and trans-substituted thietane dioxides the cycloaddition reaction is reversible202 and several further transformations are necessary if a dioxide without 3-lV-substituent is required. 

A closely related procedure for preparing thietane dioxides is the one-step conversion of cyclic a-amino ketoximes (222) to 2-(co-cyanoalkyl)-3-dialkylaminothietane dioxides (226), with trans-orientation of the substituents249 (equation 86). 

The dominant pattern for the thermal fragmentation of thietane dioxides involves extrusion of sulfur dioxide leading to a 1,3-diradical (i.e. 242) which closes to final products, mainly cyclopropanes, accompanied by rearrangement products resulting from hydrogen migration within the diradical191,1930 230,256-258 (equation 92). 

Analogous results are obtained in the pyrolysis of 3-alkylidene-2,2,4,4-tetramethylene-thietane dioxides256 (244), 3-hydroxy and 3-keto thietane dioxides (245)191, and 1,3-dithietane dioxides and tetroxides (184b and 7b)192. The extrusion of both CO and S02 and the two S02 moieties in 245b-d and 7b, respectively, to give ethylene, the formation of... 

The photolysis of various substituted thiete dioxides under similar conditions resulted in the formation of the unsaturated ketones (255)264, most probably via a vinyl sulfene intermediate followed by a loss of sulfur monoxide as shown in equation 96. The same results were obtained in the thermolysis of 6e (R1 = R3 = Ph R2 = R4 = H)231, which further demonstrates that similar mechanisms are operative in thermolyses and pho-tolyses of thietane dioxides and thiete dioxides. 

The steric effect generated by the gem-dimethyl group of the thietane ring on the adjacent sp2 carbon atom makes the cycloaddition in these cases more sluggish compared with those of the parent thietane dioxide (6b)190. These cycloadditions provide a convenient entry into the strained thiabicyclo [2.2.0] hexane system (e.g. 287, 288 equation 107). 

Chiral thietane dioxides, synthesis of 449 Chiral thiete dioxides, synthesis of 449 Chlorine compounds, as oxidizing agents... 

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

Interestingly, the crystal structures of 3-substituted thietane and thietane dioxides showed that in the solid state they exist in the puckered structure, with the S—O bond equatorial in the oxides and the 3-substituent axial for the trans-isomers, contrary to what has been quoted before . Thus, the claim that conformer 5c is predominant in the solutions of the trans-isomer needs to be re-examined. 

It is difficult to decide whether the discrepancy between the calculated and experimental data is due to a different conformational preference of the thietane dioxides in the liquid and the solid phase, or to the crude approximations included in the Karplus-Barfield equation. However, the relationship between vicinal coupling constants and dihedral angles appears qualitatively valid in thietane oxides and dioxides, particularly if trends instead of exact values are discussed . At any rate thietane dioxides, 1,3-dithietane dioxides and tetroxides maintain either planarity or a slightly distorted average vibrating conformation with a low barrier to ring planarity . 

Following a detailed NMR study of the 3-substituted thietane dioxides 188 it was concluded that the three-bond coupling constants can be safely used for stereochemical assignments in this series in particular the 7rih4<4Hz (Table 7, R =H, X = C) is consistent with an equatorial-equatorial interaction. This indicates an axial preference for the 3-substituent R (i.e. 188b) in both liquid and solid phases, and also suggests that the ring is puckered . 

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