Approaches to wine aroma: C1 transfer during the reaction between diacetyl and cysteine.

The model reaction of cysteine and diacetyl under winemaking conditions resulted in the identification of over 40 products. Of these, 12 were also identified in wine samples. Several products of the model system contained unexpected structures that do not fit the four-carbon skeletal pattern of diacetyl. Possible synthetic routes to one of these products, trimethylpyrazine, are presented.

The cysteine reaction with diacetyl under wine-like conditions: proposed mechanisms for mixed origins of 2-methylthiazole, 2-methyl-3-thiazoline, 2-methylthiazolidine, and 2,4,5-trimethyloxazole.

A part of the "bouquet of wines" can be caused by the presence of odorous heterocycles produced by chemical reactions between S-amino acids and α-dicarbonyl compounds. Under wine ageing physic-chemical conditions (20 ± 2 °C, ethanol/water 12% v/v, pH 3.5), products of the diacetyl (DI) reaction with cysteine include a number of 1,3-N,S and 1-3-N,O 5 member heterocycles having methyl groups attached at C(2). The origin of this methyl-C(2) fragment was not clear; it could be supplied from DI or from cysteine. To explore this question, a parallel reaction was run in which DI was replaced by 3,4-hexanedione. With the C(1) and C(4) carbons of DI thus marked with methyl groups, the product distribution demonstrated that in the DI and cysteine reaction, both DI and cysteine provided the methyl-C(2) to varying degrees in the formation of 2-methylthiazole, 2-methyl-3-thiazoline and 2,4,5-trimethyloxazole but only cysteine supplied this fragment for 2-methylthiazolidine. The results are interpreted in terms of reaction paths appropriate for the mild conditions. These pathways shed light on the mechanisms leading from dicarbonyls to heterocyclic compounds. Like all the chemical pathways, they anticipate the impact of other compounds and physicochemical parameters on heterocyclic generations the generation of heterocyclics. They also suggest the presence of unexplored odorous compounds.

New easy approach to the synthesis of 2,5-disubstituted and 2,4,5-trisubstituted 1,3-oxazoles. The reaction of 1-(methylthio)acetone with nitriles.

The reaction of 1-(methylthio)acetone with different nitriles in the presence of triflic anhydride led to the one-pot formation of 2-substituted 5-methyl-4-methylthio-1,3-oxazoles in good yield. 1,2- and 1,4-Bisozaxolyl-substituted benzenes were obtained when the reaction was carried out using aromatic dinitriles. The methylthio group at the C4 position of the oxazole ring was easily removed with Raney nickel to form 2-substituted 5-methyl-1,3-oxazoles in good yields. 4-Methylsulfonyl derivatives were prepared by the oxidation of the MeS group with m-CPBA. The proposed mechanism for the formation of oxazoles involves an unstable 1-(methylthio)-2-oxopropyl triflate, which was detected from the low-temperature NMR spectra.