Ethyl thioacetate

Figure 20 1 shows the structures of various derivatives of acetic acid (acetyl chlo ride acetic anhydride ethyl thioacetate ethyl acetate and acetamide) arranged m order... 

The efficiency of catalysts 86-89 for the asymmetric aldol reaction of a series of nucleophiles toward benzyloxyacetaldehyde was studied. For example, compound 89c was found to be an excellent catalyst for the asymmetric aldol reaction of silylketene acetal derivatives of t-butyl thioacetate, ethyl thioacetate, and ethyl acetate with benzyloxyacetaldehyde. In the presence of 0.5 mol% of the catalyst, the asymmetric aldol reaction took place at —78°C in CH2C12, affording the respective /i-hydroxy esters with excellent enantioselectivity (Scheme 3-32). 

An alternative route begins with 341 which is treated with ethyl thioacetate in the presence of K2CO3 and the resulting intermediate is cyclized to give 340f <1997H(45)1319> a monophenyl derivative (56%) is prepared in the same way <2005JHC661>. 

The first group of sulphur compounds mentioned above can be defined as common fermentative sulphur volatiles (CFSV) and includes in our presentation ethylmercaptan (EtSH), dimethyl sulphide (DMS), diethyl sulphide (DES), dimethyl disulphide (DMDS), diethyl disulphide (DEDS), methyl thioacetate (MTA), ethyl thioacetate (ETA), 2-mercaptoethanol (ME), 2-(methylthio)-l-ethanol (MTE), 3-(methylthio)-l-propanol (MTP), 4-(methylthio)-l-butanol (MTB), benzothiazole (BT) and 5-(2-hydroxyethyl)-4-methylthiazole (HMT) (see Table 5.6). 

Mukaiyama et al. have shown that a BINOL-derived oxotitanium catalyzes the asymmetric aldol reaction of aldehydes with thioester silyl enolates [147]. In the presence of the chiral complex (20mol%), the TBS enolate of S-t-butyl thioacetate reacts smoothly with aromatic and a,/ -unsaturated aldehydes in toluene to give silylated aldols in high yields with moderate to good enantioselectivity (91-98%, 36-85% ee). The use of the TBS enolate of S-ethyl thioacetate results in lower enantioselectivity. 

In general, DMS increases during aging (Simpson, 1979 Segurel et al., 2005), instead methyl and ethyl thioacetates hydrolyze, and there is an increase of thiols and disulfides observed (Rauhut, 1996). Another sulfur compound found in wine is bis(2-hydroxyethyl)disulfide, which was found in extracts of wines, in particular from Vitis labrusca grapes or its hybrids (Anocibar Beloqui et al., 1995). This compound is a precursor of H2S and 2-mercaptoethanol, two substances with a very strong rotten egg and unpleasant poultry-like odor, respectively. After... 

Figure 5.2. Volatile sulfur compounds of wines (15) dimethyl sulfide, (16) ethylmer-captan, (17) diethyl sulfide, (18) methyl thioacetate, (19) dimethyl disulfide, (20) ethyl thioacetate, (21) diethyl disulfide, (22) 2-mercaptoethanol, (23) 2-(methylthio)-l-ethanol, (24) 3-(methylthio)-l-propanol, (25) 4-(methylthio)-l-butanol, (26) 3-mercap-tohexan-l-ol, (27) 4-methyl-4-mercaptopentan-2-one, (28) 3-mercaptohexanol acetate, (29) benzothiazole, (30) 5-(2-hydroxyethyl)-4-methylthiazole, (31) fra s-2-methylthio-phan-3-ol, (32) 2-methyltetrahydrothiophen-3-one.

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