Sulfenes generation

Dienamines undergo 1,4 cycloaddition with sulfenes as well as 1,2 cycloaddition. For example, l-(N,N-diethylamino)butadiene (111), when treated with sulfene (generated from methanesulfonyl chloride and triethyl-amine), produces 1,4 cycloadduct 116 in an 18 % yield and di-1,2-cycloadduct 117 in a 60 % yield (160). Cycloadduct 116 was shown not to be the precursor for 117 by treating 116 with excess sulfene and recovering the starting material unchanged (160). This reaction probably takes place by way of zwitterion 115, which can close in either a 1,4 or 3,4 manner to form cycloadducts 116 and 118, respectively. The 3,4 cycloaddition would then be followed by a 1,2 cycloaddition of a second mole of sulfene to form 117. Cycloadduct 117 must form in the 3,4 cycloaddition followed by a 1,2-cycloaddition sequence rather than the reverse sequence since sulfenes undergo cycloaddition only in the presence of an electron-rich olefinic center (159). Such a center is present as an enamine in 118, but it is not present in 119. 

A similar intramolecular nucleophilic capture of an allylic sulfenate generated thermally from the corresponding sulfoxide was also reported for the facile transformation of the azetidinone 61 into a new 3-acetylthio-2-thiacephem ring system 62 (equation 29)127. 

Cycloaddition of ynamines with sulfenes (generated from sulfonyl chlorides) to give thiete sulfones 132 and 133 has been reported by Truce et (Eq. 21). Acid hydrolysis yields the corresponding enols (134). Other compounds that have been prepared in this manner are 135 and 136. Sulfene... 

Sulfenes, generated in situ from alkylsulfonyl chlorides and triethylamine, react with thiatriazoline (50) to give sultams (53). The sultams isomerize on heating at 60 °C in the presence of benzoyl chloride, or A1C13 and methanesulfonyl chloride (equation 24). 

Carboxylic anhydrides. Carboxylic acids can be converted into the anhydrides by reaction with sulfene (generated from methancsulfonyl chloride and triethylaminc). Yields are in the range 82-95%. 

Sulfenes generated from sulfonyl chlorides and tertiary amines do not react with simple alkenes or dienes however, the sulfene generated from (trimethylsilyl) methanesulfonyl chloride (112) and caesium fluoride affords the [4+2] cycloadduct (113) with cyclopentadiene (114) (Scheme 73). 

Another example is the conversion of cyclohexene (164) to the bicyclic sultone (165) (Scheme 67). This allows the synthesis of sultones with partially determined stereochemistry. Both reactions depend on the high leaving group properties of the methanesulfoxy anion. Unsaturated 8-sultones like (166) can be obtained by 1,4-cydoaddition of sulfenes (generated in situ) to a,(3-unsaturated carbonyl compounds (Scheme 68). 

Wells and Abbott186 carried out a systematic study of the addition of sulfene generated from methanesulfonyl chloride and triethylamine to various enamines in ether and acetonitrile. They found that both cyclic and acyclic products were produced in these solvents. 

Several groups202-204 reported almost simultaneously that sulfenes, generated from sulfonyl chlorides and triethylamine, also react with the acetylenic analogue of enamines (i.e. ynamines or alkynylamines) to give a mixture of the dialkylaminothiete 1,1-dioxides (equation 92). Block and Aslam98 reported that sulfene generated from... 

Sulfenes generated from alkanesulfonyl chlorides and tertiary amines have not been observed to react with simple olefins or dienes1,36, but Block and Aslam98 reported that sulfene from (trimethylsilyl) methanesulfonyl chloride with cesium fluoride reacted with dienes to afford [4 + 2] cycloadducts (equation 110). Slightly greater yields of the... 

Rai and coworkers213 have claimed that reaction of sulfene, generated from methane-sulfonyl chloride and triethylamine, with benzylideneanilines afforded 1,4-benzothiazine 1,1-dioxides (131) in good yields (equation 120), and suggested that 131 resulted from rearrangement of an initial [2 -l- 2] cycloadduct 129 (equation 121). 

The reaction of chloral with sulfene generated from methanesulfonyl chloride and triethylamine has been found to give jS-sultone (equation 134)219,22°. It was observed156 that... 

Hanefeld and coworkers179 have recently noted that the reaction of sulfenes generated in situ from sulfonyl chlorides and tertiary amines, with vicinal tricarbonyl compounds such as indan-l,2,3-trione, alloxane, diethyl mesoxalate and 1-methyl-1,2,3,4-tetrahydroquinoline-2,3,4-trione, afford products derived mainly from ring opening of /i-sultones (equation 139). 

The interaction of 4-alkyl-5-arylimino-l,2,3,4-thiatriazoline (69) and sulfenes (generated in situ from alkylsulfonyl chlorides and triethylamine82) produces sultams (72), possibly by way of the heteropentalenes (71) these isomerize above 60°C under the influence of acidic catalysts to 73, by a Dimroth rearrangement.77 The sultams (72) are themselves capable of acting as masked 1,3-dipoles, undergoing cycloaddition with heterocumulenes, with elimination of the sulfene moiety. Thus reaction of 72 with phenyl isocyanate produces the 1,2,4-thiadiazolidine (70), also directly accessible from 69 by Path A.83... 

Reaction of sulfene generated from methanesulfonyl chloride with triethylamine in the presence of a pyridine derivative resulted in (266) (Equation (56)). The methylene protons could be exchanged with deuterium <78CJC1183>. 

In the reaction of the enamine derived from isobutyraldehyde and sulfene, generated from diazomethane and sulfur dioxide, the [2-1-2] cycloadduct 14 (9-18 %) and the [2-I-2-I-2] cycloadduct 15 (2-26 %) are obtained. ... 

Mixtures of tautomeric [2-1-2] cycloadducts are obtained in the reaction of several sulfenes, generated in situ, with l-diethylaminopropyne. ... 

The unsaturated sulfene, generated from 1-propenesulfonyl chloride and triethylamine, reacts with ketene diethylacetal to give the [2+2] cycloadduct 18 and a [4+2] cycloadduct 19. 

Also, azomethine imines 28 react with sulfenes, generated from the corresponding sul-fonyl chlorides and triethylamine, to give 1,2,3-thiadiazolidines 29" . 

Perhaps one of the most important reactions involving sulfur dioxide is the retro-reaction, which affords olefins and sulfur dioxide. A review article on the formation of olefins from sulfenes, generated from diazo compounds and SO2, was published by Fischer in 1970 . 

Cycloadditions [2+2] Cycloaddition reactions of sulfur dioxide to double-bonded substrates are rare. An example is the addition to the C=S bond in sulfenes, generated in situ. However, the cycloadduct 4 loses S2O3 to form a ketone. ... 

Heterocycles. Sulfene, generated by the treatment of methanesulfonyl chloride with base, undergoes [2 + 2], [3 + 2], and [4 + 2] cycloadditions to produce four-, five-, and six-membered heterocycles, respectively. Alkynyl amines and enamines both undergo [2 + 2] cycloadditions with sulfene to produce four-membered cyclic sulfones (eqs 19 and 20). 

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