Alkyl thiosulfinates

Thermolysis of alkyl thiosulfinates in the presence of added alkynes or... 

Only a few intramolecular thioaldehyde [4 + 2] cycloadditions have been executed to date. Vedejs et al. have looked at systems such as that shown in equation (88).Their photochemical method is useful in effecting intramolecular reactions but stereoselectivity in the process was only moderate. Baldwin and Lopez have described the single intramolecular cycloaddition shown in equation (89) which involves a new thermal method for generating thioaldehydes from alkyl thiosulfinates. ... 

The polarimetric method, in combination with the results of chemical correlation, made it possible to determine the optical purity of a range of chiral sulftnates (105-107), thiosulfinates (35,105), and sulfinamides (83) with the sulfur atom as a sole center of chirality. These compounds were converted by means of Grignard or alkyl-lithium reagents into sulfoxides of known specific rotations. This approach to the determination of optical purity of chiral sulfinyl compounds has at least two limitations. The first is that it cannot be applied to sterically hindered compounds [e.g., t-butyl /-butanethio-sulfinate 72 does not react with Grignard reagents]. Second, this... 

The most important flavour compound in raw onions is thiopropanal-S-ox-ide, the lachrymatory factor [145,146]. Other important flavour compounds are 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene and alkyl alkane thiosulfonates such as propyl methanethiosulfonate and propyl propanethiosulfonate with a distinct odour of freshly cut onions [35, 36, 147]. Various thiosulfinates that have a sharp and pungent odour may also contribute to the flavour of onions. These compounds, however, are rapidly decomposed to a mixture of alkyl and alkenyl monosulfides, disulfides and trisulfides (Scheme 7.3) of which dipropyl disulfide, methyl ( )-propenyl disulfide, propyl ( )-propenyl disulfide, dipropyl trisulfide and methyl propyl trisulfide are the most important contributors to the aroma of raw and cooked onions (Table 7.5, Fig. 7.6) [148-150]. Recently, 3-mercapto-2-methylpentan-l-ol was identified in raw and cooked onions eliciting intense meat broth, sweaty, onion and leek-like odours [142, 151]. 

In the case of the oxidation of methyl alkyl sulfides, enantioselectivity remains in the range of 50-60% ee (Table 6C.2). Disufides R-S-S-R, sulfenamides R-S-NR 2, and sulfenates R-S-O-R were oxidized to the corresponding chiral thiosulfinates, sulfinamides, and sulfinates, respectively (<52% ee, Table 6C.3) [21]. 

Bass, S.W. and Evans, S.A., Jr., Carbon-13 nuclear magnetic resonance spectral properties of alkyl disulfides, thiosulfinates, and thiosulfonates, J. Org. Chem., 45, 710, 1980. 

In analogy to hydroformylation, alkenes react with SO2 and H2 to give a so-called hydrosulftnation product, sulfinic acids [116]. Cationic Pd(II) and Pt(II) complexes bearing bidentate phosphine ligands are effective catalyst precursors. A plausible mechanism for the hydrosulfination involves formation of alkyl intermediates by olefin insertion into metal hydrides, subsequent insertion of SO2, and reformation of the hydrides with the release of sulfinic acids (Scheme 7.19). However, ahphatic sulfinic acids readily undergo disproportionation to give thiosulfinic acid esters, sulfonic acids, and water at the reaction temperature. The unstable sulfinic acids can be conveniently converted into y-oxo sulfones by addition of a,-unsaturated carbonyl compounds as Michael acceptors to the reaction mixtine (Eq. 7.23) [117]. 

The mechanism of flavor formation from the alkyl cysteine sulfoxide (alhin) is outlined in Figure 4.13. While the initial steps of this pathway are enzymatic, reactions beyond sulfenic acid are purely chemical in nature. Sulfenic acid is extremely reactive, readily forming the unstable thiosulfinate intermediate by reaction with a second sulfenic acid molecule. This thiosulfinate decomposes to form a relatively stable thiosulfonate and mono, di- and trisulfldes. Considering that several different aUcyl precursors are available in each Allium species, a host of different mono-, di-, and trisulfides can be formed via different sulfenic acid combinations. It is these mono-, di-, and trisulfides that are most important in determining typical Allium flavor. 

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