Thiete 1,1-dioxides

In view of the limited capacity of the sulfur atom in the sulfoxide and sulfone functional groups to transmit conjugative effects due to the insulating effect of the LUMO sulfur d-orbitals45,46,56, the application of the UV technique even in the case of the cyclic vinyl sulfones (e.g. thiete dioxides 6b) cannot be expected to find extensive use. UV spectra of substituted thiete dioxides in which an extended conjugated system (e.g. 194) exists in the molecule, did provide useful information for structure elucidation231. However, the extent... 

Thiete dioxides, in which the double bond is incorporated into an aromatic system (i.e. 234), are made via the same strategy depicted in equation 87, except that the system is aromatized only at the last step250-253 (equation 89). 

Asymmetric induction and the synthesis of optically active thietane and thiete dioxides can be achieved via the basic strategy depicted above (equation 87), by using optically active enamine in the first (2 + 2) cycloaddition187 (equation 90). [Pg.449]

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. 

Based on the high dienophilicity of acyclic vinyl sulfones one should expect thiete dioxides to exhibit similar properties. Indeed, several Diels-Alder (2 +4) cycloadditions with thiete dioxide as dienophile are known. For example, 1,3-butadiene and 1,3-diphenylisobenzofuran react with 3-chloro- or 3-bromo-thiete dioxides to afford the corresponding 1 1 Diels-Alder cycloadducts255 277 (equation 105). 

As expected, 1 1 (2 + 2) cycloadducts are obtained in the reactions of thiete dioxides with some typical electron-rich olefins, e.g. enamines and ynamines, although this cycloaddition has not proven to be general190. 

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 . ... 

A preparation of 3-substituted thiete dioxides takes advantage of the commercial availability of the parent four-membered thietanes. The latter is oxidized to the sulfone, which in turn is photochemically mono- or di-chlorinated in the 3-position. The 3-chlorothietane dioxide (239a) can be easily transformed into the thiete dioxide, whereas the 3,3-dichloro homolog is transformed into the 3-chloro-2H-thiete 1,1-dioxide (240b) (equation 91). 240b reacts with carbanions, amines, alcohols and thiols to give the corresponding 3-substituted thiete dioxides. ... 

The formation of cyclic sulfinic esters (sultines) from vinyl sulfenes is known , and the trapping of the expected intermediate vinyl sulfene in the thermolysis of thiete dioxide (6fc and 194) has been convincingly achieved . Specifically, thermolysis of thiete dioxide 6b in the presence of norbornenes gave cycloadducts of the Diels-Alder type (i.e. 252b), resulting from the trapping of the vinyl sulfene formed. The accumulated evidence thus supports the proposed mechanism for these thermolytic reactions. 

Base-induced eliminative ring fission, in which both the double bond and the sulfone function take part, has been observed in thiete dioxides . The reaction can be rationalized in terms of initial Michael-type addition to the double bond of the ring vinyl sulfone, followed by a reverse aldol condensation with ring opening. The isolation of the ether 270c in the treatment of 6c with potassium ethoxide (since the transformation 267 268 is not possible in this case) is in agreement with the reaction mechanism outlined in equation 101 . 

Cycloadditions of nitrones, nitrile oxides or diazo compounds to thiete dioxides do not show the high stereoselectivity observed with acyclic vinyl sulfones, and mixtures of the two possible adducts are formed . The charge-transfer stabilization energy calculated according to the Klopman-Salem perturbational approach is able to account for the experimental trends of the isomer ratio in terms of the major stereochemical structural differences between the acyclic vinyl sulfones and the four-membered ring sulfones (see Section IV.B.3). 

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