Dithietane-1,1-dioxide

A few special syntheses of thiirane derivatives from four-membered sulfur heterocycles are known. Methylenethiiranes are derived by thermolysis of the tosylhydrazones of thietan-3-ones (Scheme 143) (81TL4815), and 2,2,3,3-tetrakis(trifluoromethyl)thiirane is obtained by thermolysis of 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dithietane 1,1-dioxide with loss of sulfur dioxide. 2,2,3,3-Tetrakis(trifluoromethyl)thiirane 1,1-dioxide is obtained in low yield by heating a mixture of 3,3-bis(trifluoromethyl)-l,2,4-oxadithietane 2,2,4,4-tetroxide and bis(trifluoromethyl)ketene. The mono-episulfide of norbornadiene is obtained from thietane derivative (65 Scheme 144) (73JOC649). 

Tlie chemistry of 1,2-dithietanes is still emerging. Isolable and well-characterized 1,2-dithietanes are limited to only two compounds, 3,4-diethyl-l,2-dithietane 1,1-dioxide (77) and dithiatopazine (73).The synthesis of 1,2-dithietanes has been overshadowed by their thermal instability, which arises most probably from repulsive interactions between the lone-pair electrons on the sulfur atoms, as we have already seen in the chemistry of dithiiranes. 

Similarly, a series of thial 5-oxides 83 dimerized upon standing to give 1,2-dithietane 1,1-dioxides 84, which were reduced to the corresponding alkenes on treatment with LiAlFLt (93SL839 96BSF515). 

Stereoselective conversion of 3,4-disubstituted-l,2-dithietane 1,1-dioxides 114 into symmetrical (Z)-alkenes 115 has been reported. When substituted 1,2-dithietane 1,1-dioxides 114 having a reactive thiosulfonate group in the four-membered ring were treated with lithium cyanide, the alkenes 115a-d were obtained with high (Z)-selectivity and high chemical yield (Equation 15) <1996BSF515>. 

The intermediacy of 1,2-dithietanes has been proposed in several transformations . The isolable and well-characterized 1,2-dithietane 1,1-dioxides 40 are synthesized via a cycloaddition reaction of methanethial -oxides 39 (Scheme 30) <1996JA7492>. 

The lachrymatory factor of onions, propanethial 5-oxide, dimerizes slowly in a benzene solution in the dark to form /ra .y-3,4-diethyl-l,2-dithietane 1,1-dioxide (12)122. 

The only well-characterized, stable 1,2-dithietane derivative is 3,4-diethyl-1,2-dithietane 1,1-dioxide 525, obtained by dimerization of propanethial 5-oxide. The C and nmr chemical shifts have been determined ring-carbon atoms 6 39.2, 97.9ppm 210 and 243ppm in acetone relative to water. A 1,2-... 

A few syntheses of thiiranes from four-membered sulfur-containing heterocycles are reported. 2,2,3,3-Tetrakis(trifluoromethyl)thiirane is yielded by thermolysis of 2,2,4,4-tetrakis-(trifluoromethyl)-l,3-dithietane 1,1-dioxide with loss of sulfur dioxide (Equation (38)) <61USP3136781>. 

The principal component of the lachrymatory factor of the onion (Allium cepa) has been identified by flash vacuum pyrolysis (FVP)/microwave techniques as (Z)-propanethial 5-oxide, CH3CH2CH=S=0. It functions as a 1,3-dipole and as a dipolarophile, and it dimerizes in cold benzene to give principally trans-3,4-diethyl-1,2-dithietan 1,1-dioxide rather than 2,4-diethyl-1,3-dithietan 1,3-dioxide, as previously proposed. Formation of this sulphine from its cellular precursor, rran5-(+)-S-(prop-l-enyi)-L-cysteine sulphoxide, is suggested to involve the formation of a Schiff base and the elimination of ( )-prop-l-enesulphenic acid, which then rearranges to the sulphine (Scheme 2). 

In contrast to the sulfenes, the [2-1-2] cycloaddition reactions of sulfines are not well known. The dimerization of ethylsulfine gives rise to a four-membered ring rra 5-3,4-diethyl-l,2-dithietane 1,1-dioxide, which is not the result of a [2-1-2] cycloaddition Similarly, reaction... 

The mechanism of formation of the dithietane 1,1-dioxide dimers involves an opposite [3-1-2] cycloaddition to form 3, which subsequently rearranges to give 4... 

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