Sulfene, generation from

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. 

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... 

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). 

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... 

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. ... 

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 . 

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. 

Saito et al. <1995S87> described a new method for the synthesis of heterocycle-fused[c]thiophenes via reaction of aryl heteroaryl thioketones with the carbene precursors. Heteroaromatic thioketones A react with carbenoids generated from bis(arylsulfonyl)diazomethanes or phenyliodonium bis(phenylsulfonyl)methylides to give heterocycle-fused[f]thiophenes B. The reaction involves the ring closure of the intermediary thiocarbonyl ylides, followed by restorative aromatization via the elimination of a sulfenic acid (Equation 11). 

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). 

Reaction of heteroaromatic thioketones 638 with the carbenoids, generated from phenyliodonium bis(phenylsul-fonyl)methane or bis(arylsulfonyl)diazomethanes in the presence of a copper acetylacetonate catalyst, affords heterocycle-fused [c]thiophenes 639. The reaction involves ring closure of the intermediary thiocarbonyl ylides and elimination of a sulfenic acid (Equation 33) <1995S87>. 

The sulfenic acids usually generated in this way are very unstable and react instantaneously with alkenes present in the reaction medium to form sulfoxides88,89. A number of reversible intramolecular cyclic eliminations of sulfenic acids from cyclic sulfoxides have been reported, for example, thiepane 1-oxide decomposes at 140 C with a half-life of ca. 28 hours to give cis-2-methyTtetrahydro-2//-thiopyran l-oxide (1), which is stable under these conditions for 6 days90. 

As discussed previously, treatment of thiolates generated from thiols and MeLi with sterically hindered A -sulfonyl-oxaziridine 116 gave the corresponding sulfenate intermediates which were alkylated to afford sulfoxides 118 (Equation 4) <1997JOC8626, 1999PS(153)381, 2004JOC6916>. Oxidation of thiolates generated from aryl thiols... 

Sulfene (75), generated from methanesulfonyl chloride and triethylamine, reacts with the cyclohexanone enamine (99) to give the four-membered cyclic amino sulfone (100) (Scheme 67) (see Chapter 10, p. 210). 

The first addition of a sulfene to a carbon-nitrogen double bond was reported by Staudinger and Pfenninger (1916), who demonstrated that diphenylsulfene (119) generated from diphenyldiazomethane (120) and sulfur dioxide, reacts with benzylideneaniline (121) to give the four-membered [2+2] cycloadduct (122) (Scheme 75). 

Sulfenes (see Chapter 7, p. 114) generated from sulfonyl chlorides by treatment with a tertiary amine may be used to prepare p-sultams. Thus, the sulfonyl chloride (184) may be converted to the sultam (185) via the sulfene (186) by reaction with an activated alkene (Scheme 77)... 

Sulfonyl imides(RN=S02), generated from alkylsulfamoyl chloride (RNHSOjCl) and triethylamine, react with enamines in the same way as sulfenes do, to give four-membered heterocycloadducts such as 210 Phenyl isocyanate undergoes [2 -t- 2] cycloaddition with enamines affording azetidinones (211) whereas azetidinothiones (212) have been obtained from the reaction of isothiocyanates with enamines without j8-hydrogens . ... 

The 4-penten-l-oxyl radical (5) has been generated from the corresponding nitrite [39, 40], hydroperoxide [41], peroxycobaloxime [42], benzene (9-sulfenate... 

Stork and Borowitz36 were able to rule out an alternative mechanism, in which an initially formed mesylated enamine underwent cyclization, by preparing the mesylated species (87) and showing that it did not yield the cycloadduct (equation 67). Borowitz36 also demonstrated that only electron-rich olefins (such as enamines, ketene dialkyl acetals, etc.) give [2 + 2] cycloadducts when the sulfene is generated from alkenesulfonyl chlorides and triethylamine, and no cycloadduct was formed in the presence of cyclohexene, ethoxyacetylene or anthracene. 

Shipov and collaborators80 have recently found that (trimethylsilyl)sulfene (93) generated from (trimethylsilyl)methanesulfonyl chloride and triethylamine reacts with an isobutyraldehyde enamine to give a mixture of cis and trans cycloadducts 94a and 94b (equation 74). 

The first cycloaddition of sulfene to the C=N bond was reported by Staudinger and Pfenninger107, who showed that the reaction of diphenylsulfene, generated from diphenyldiazomethane and sulfur dioxide, gave a four-membered cyclic compound with benzylideneaniline (equation 118). 

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... 

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