Allyl sulfenic acid

In the presence of a suitably disposed /i-hydrogen—as in alkyl-substituted thiirane oxides such as 16c—an alternative, more facile pathway for thermal fragmentation is available . In such cases the thiirene oxides are thermally rearranged to the allylic sulfenic acid, 37, similarly to the thermolysis of larger cyclic and acyclic sulfoxides (see equation 9). In sharp contrast to this type of thiirane oxide, mono- and cis-disubstituted ones have no available hydrogen for abstraction and afford on thermolysis only olefins and sulfur monoxide . However, rapid thermolysis of thiirane oxides of type 16c at high temperatures (200-340 °C), rather than at room temperature or lower, afforded mixtures of cis- and trans-olefins with the concomitant extrusion of sulfur monoxide . The rationale proposed for all these observations is that thiirane oxides may thermally... 

There are several reactions in which the sulfoxy oxygen exhibits its nucleophilicity, the most noticeable being the thermal rearrangement of thiirane oxides (in the presence of a suitable disposed 8-hydrogen) to allylic sulfenic acids (see equation 9 in Section III.C.l). 

The thermolysis of acyclic- and/or six- and larger ring sulfoxides to yield olefins and sulfenic acids is well documented . The formation of allylic sulfenic acids and thiosulfinates in the thermolysis of thiirane oxides containing hydrogen on the a-carbon of the ring substituent (which is syn to the S—O bond) has been discussed previously in terms of /i-elimination of hydrogen, which is facilitated by relief of strain in the three-membered ring (Section llI.C.l). 

Although no direct experimental evidence was reported for a perepoxide intermediate, episulfoxide [51], an analogous compound of perepoxide, has been prepared and rearranged at 25°C to the allylic sulfenic acid ... 

Similar to the S-allyl-L-cysteine sulfoxide in garlic, the C-S lyase can also catalyze the flavor formation from the 5 -methyl-L-cysteine sulfoxide. Therefore, when garlic is cut or crushed, methyl sulfenic acid and allyl sulfenic acid can be produced from 5 -methyl-L-cysteine sulfoxide and S-allyl-L-cysteine sulfoxide, respectively (Figure 18.5). As sulfenic acids are quite reactive, methyl sulfenic acid and allyl sulfenic acid will quickly form the metiiyl 2-propenethiosulfinate and allyl methaneth-iosulfinate. With the similar reaction to that from diallyl thiosulfinate, these thiosulfinates produce allyl methyl disulfide and allyl methyl trisulfide. 

An interesting procedure has been developed by Vat le to obtain C-5 branched-chain sugars [189]. It also takes advantage of the stereospecificity of the Claisen rearrangement of allyl (vinylsulfinyl) ether 158 derived from a 4,5-unsaturated sugar. An acrylic derivative 159 is formed in the process by elimination of sulfenic acid (Scheme 53). 

Hydrolysis of perfluoro-3-isopropyl-4-methylpentenyl-2-sulfenyl chloride 34 having a mobile allyl fluorine atom ends with the formation of perfluoro-2,4,4-trimethyl-3-isopropylthiete 35 (yield 30%) (89IZV1380). The reaction occurs via the intermediate formation of the derivative of sulfenic acid 36 due to the high mobility of the allylic fluorine atom. 

The cleavage of the intermediate allyl sulfenate can also be initiated under acidic conditions, e.g., by using catalytic amounts of 4-toluenesulfonic acid in ethanol or with thiophenol in dioxane5. By a combination of this method with the selenium dioxide catalyzed oxidation of allylic sulfides, a one-pot transformation of allylic sulfides to rearranged allylic alcohols was achieved. 

Heating allyl 2-naphthalenyl sulfoxide (7) to 120 CC for 2 hours in dimethylformamide results in quantitative isomerization to the cw-dihydrothiophene derivative 8. A possible pathway for the formation of 8 involves [3,3] sigmatropic rearrangement of 7 to a thioketone S-oxidc followed by a [1,4] sigmatropic rearrangement to a sulfenic acid intermediate and final intramolecular cis addition to give 889 92. 

The addition of an allyl alcohol to racemic allenyl sulfoxides results in vinyl ethers with the sulfinyl moiety at C-1 that undergo sigmatropic rearrangements upon distillation to produce 2,4-dienones after ehmination of sulfenic acid. In one example, an isomeric vinyl ether was obtained with a sulfinyl methyl substituent at C-2 that gave rise to a sulfinyl enone upon rearrangement [138]. In related work, the addition-elimination of an allyl alkoxide to a functionalized vinyl sulfoxide results in a sulfinyl enol ether that rearranges with loss of sulfenic acid to the unsaturated ester [139-141] (Scheme 21). 

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... 

The oxidation of allylic sulfides with equivalent amounts of, for example, peroxyacids or sodium per-iodide leads to allylic sulfoxides. These sulfoxides do not usually eliminate sulfenic acid to provide... 

The flavor precursors, 5 -alk(en)yl-L-cysteine sulfoxides, themselves do not have any specific flavor. However, when garlic or onion cells are damaged by cutting or crushing and the 5 -alk(en)yl-L-cysteine sulfoxides meet the C-S lyase (alliinase), they are converted into various volatile sulfuric compounds. Stoll and Seebeck (1951) first proposed the production of diallyl thiosulfinate (allicin) from the 5 -allyl-L-cysteine sulfoxide (alliin) by the C-S lyase. Through the reaction catalyzed by the C-S lyase, 5 -alk(en)yl-L-cysteine sulfoxides yield alk(en)yl sulfenic acid and aminoacrylic acid, the latter being spontaneously degraded... 

On treatment with camphorsulfonic acid/pyridine, methyl ( )-1-[(.S )-4-mcthylphcnylsuirinyl]-2-alkenoates undergo, enantioselectively, a sequential prototropic shift and allylic sulfoxide/ sulfenate rearrangement to produce methyl (R,/f)-4-hydroxy-2-alkcnoates in 64- 72% optical purity63a. 

Lithiated allyl sulfide 256-Li reacted with m-xylylene dibromide 257 to afford the bis-sulfide 258. A double Mislow-Evans rearrangement of 258 and subsequent reductive trapping of the sulfenate ester provided the symmetric trans-diol 255. Monoprotection, Sharpless asymmetric epoxidation, and reductive ring-opening of the epoxide gave 1,3-diol 259 in 97% ee. After several functionalizations, the arene was subjected to Birch reduction to provide 1,4-cyclohexadiene 254. Ozonolysis of the diene, followed by reductive workup and treatment of the resulting 1,3-diketone with acid furnished pyra-... 

---