Dimethyl thiosulfinate

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]. 

Dimethyl acetylenedicarboxylate (DMAD) is able to trap both products of the reversible thermal 1,3-dipolar cycloreversion. With an excess of DMAD at 60 °C without solvent, the product 247 (Ar = Ph) arising from thiosulfine was formed in 83% yield, and the benzothiopyran 248 arising from the thiobenzophenone in 68% yield. With R = C1, yields were slightly lower (Scheme 77) <1997T939>. 

The transformation products of allicin and odier thiosulfinates present in crushed garlic is greatly accelerated and expanded upon heating such as during steam distillation or cooking. As many as 20 different sulfides have been identified in the steam distillate and include diallyl mono to hexasulfides, allyl methyl mono to hexasulfides dimethyl mono to hexasulfides, and allyl 1-propenyl di and trisulfides [38]. 

Related Reagents. Benzenesulfenyl Chloride 2-(Methyl-thio)- li/-isoindole-1,3(2/ -dione N- ferf-Butylthiophthalimide 7V-Phenylthiophthaliinide Dimethyl(methylthio)sulfoniumTetra-fluoroborate Ethyl Thiosulfinate Disulfur Dichloride. 

The volatile oil contains allicin (diallyldi-sulfide-5-oxide diallyl thiosulfinate), allyl-propyl disulfide, diallyl disulfide, and diallyl trisulfide as the major components, with lesser amounts of dimethyl sulfide, dimethyl disulfide dimethyl trisulfide, allylmethyl sulfide, 2,3,4-trithiapentane, bis-2-propenyl... 

Proteus mirabHis and Proteus vu aris reduced the same sulfoxide with opposite enantioselectivity [121]. The resolution of racemic aDcylaryl sulfoxides and thiosulfi-nates by dimethyl sulfoxide reductase from the anaerobic bacterium Citrobacterbmaldi gave the corresponding enantiopure alkylaryl sulfoxides and thiosulfinates [122]. 

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