Oxides and dioxides

Shizawa, Y. Ban, and T. Oishi, Chem. andPharm. Bull. (Japan), 1971,19, 

Aqueous sodium hydrogen sulphite and iodide ions reduced thiolan 1-oxide to thiolan much faster than they reduced the six- and seven-membered analogues to the corresponding sulphides. The reactions 

2-benzylidenethiolan 1,1-dioxide, but the threo-isorast was inert under these and more drastic conditions, presumably because /m 5-elimination of the elements of hydrogen chloride was inhibited by steric interactions between the sulphonyl and phenyl groups in the transition state, as in analogous acyclic systems.  

The equatorial protons at C(2) in (89) exchanged with deuterium 1.6 times faster than did their geminal axial protons, in [ Hgldimethyl sul-phoxide- HgO-NaO H solution. This was in accord with recent MO 

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The first substituted thiirene dioxides21 and thiirene oxides22 (e.g. 4 x = 2 and x = 1, respectively) were synthesized and characterized by Carpino and coworkers, while the parent thiirene oxide and dioxide are not known to date. However, the successful syntheses of the substituted unsaturated systems 4 opened the door to an extensive research involving the theoretical and experimental aspects of this class of intriguing compounds2, particularly as far as the unique role and characteristics of their sulfone and sulfoxide groups are concerned. 

The geometric parameters of the three-membered ring sulfones and sulfoxides have been determined via X-ray diffraction techniques and gas-phase microwave spectroscopy. The accumulated data for some selected thiirane and thiirene oxides and dioxides (16-19) as well as for the corresponding thiirane (20) and the acyclic dimethyl sulfone (for the sake of comparison) are given in Table 3, together with the calculated values. 

Analogous effects may allow aromatic assignments to the thiirene 1-oxide and dioxide, and may be demonstrated through the interaction diagrams given below52. 

The following features associated with the sulfoxide and sulfone functional groups in thiirane and thiirene oxides and dioxides are to be discussed ... 

The (formal) Michael addition of nucleophiles to thiirene oxides and dioxides (formally vinyl sulfoxides and sulfones). 

The issue of the acidity of a-hydrogens in thiirene oxides and dioxides is dealt with only in the dioxide series, since neither the parent, nor any mono-substituted thiirene oxide, is known to date. Thus the study of the reaction of 2-methylthiirene dioxide (19c) with aqueous sodium hydroxide revealed that the hydroxide ion is presumably diverted from attack at the sulfony 1 group (which is the usual pattern for hydroxide ion attack on thiirene dioxides) by the pronounced acidity of the vinyl proton of this compound113 (see equation 14). 

To summarize under favorable conditions the acidity of a-hydrogens facilitates the generation of a-sulfoxy and a-sulfonyl carbanions in thiirane and thiirene oxides and dioxides as in acyclic sulfoxides and sulfones. However, the particular structural constraints of three-membered ring systems may lead not only to different chemical consequences following the formation of the carbanions, but may also provide alternative pathways not available in the case of the acyclic counterparts for hydrogen abstraction in the reaction of bases. 

The structures of four-membered rings are of considerable interest, owing in part to the low-frequency ring puckering vibration203. The comparison of the structures and conformational preferences of thietane oxides and dioxides discussed above with those of dithietane oxides and dioxides is therefore appropriate and will follow. 

Carbon-13 chemical shifts of the a- and (8-carbon atoms of various unsubstituted and 3-substituted thietane oxides and dioxides have been recorded and correlated by the equations S = ay + bx and Sf = ax + by where a and b are parameters characteristic of the sulfoxide or sulfone (y) and the substituent (x)216. The values of the substituent parameters were found to parallel those which determine the effect on the 13C chemical shifts when hydrogen is replaced by a substituent224. 

It is noteworthy that in spite of the demonstrated acidity of the a-hydrogens in thietane oxides and dioxides, attempted mono- or dialkylations of these systems have been unsuccessful thus far. 

Thiophene oxides and dioxides have recently been thoroughly reviewed280,281. 

The existence or nonexistence of conjugative effects involving the sulfone group in thiophene dioxides (a problem analogous to that in thiirene oxide and dioxide systems2,1 ) has been the subject of many studies resulting, nonetheless, in no unequivocal conclusion280. 

Two attractive routes to thiolene oxide and dioxide are the diene-SO104 and diene-S02298 cycloadditions, respectively. These cycloadditions are highly stereoselective at both carbons of the diene systems and at sulfur (see equation 62 for specifics) which, in the case of sulfoxide formation, proceed via attack of triplet SO on the diene. Equation 112 shows an example of such a cycloaddition104. The overall yields are significantly improved by running the cycloadditions in the absence of oxygen and by the use of excess diene. 

Since sulfoxides and sulfones are versatile synthetic intermediates, and since in both the thiolene oxide and dioxides the reverse dethionylation114 ( — SO), and cheletropic extrusion of sulfur dioxide296, respectively, readily take place thermally, these cycloadditions are expected to find a useful place in organic synthesis. It should be kept in mind, however, that the retrograde SO-diene reaction and interconversion of the thiolene oxides compete effectively against SO extrusion on heating, and that diene isomerization accompanies the forward reaction (SO + diene). 

The cycloaddition reactions of thiophene oxides and dioxides (290 and 291280,281) have already been discussed (Section V.A). 

The trapping of both sulfines and sulfenes with dienes is probably the method of choice for the preparation of 3-thiene oxides and dioxides, respectively143,337. 

Note Only a few simple examples of the metal complexes formed by quinoxaline oxides and dioxides are given here. 

Small ring compounds represent a fair portion of strained organic systems in which the geometry of sp and that of sp carbons have been distorted from the ideal configurations. Foremost among these reactive molecules are the small ring heterocycles, such as thiirane and thiirene oxides and dioxides. ... 

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 . ... 

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