Reaction with thioacetic acid

Diphenylcyclopropene thione (156) was prepared11S-12°) from 3,3-dichloro-1,2-diphenyl cyclopropene (154) by reaction with thioacetic acid, since transformation of the carbonyl function of diphenyl cyclopropenone with P4S10121 was complicated by ring expansion to the trithione 155122 In a useful recent thioketone synthesis123) 156 was obtained directly from diphenyl cyclopropenone in a quantitative yield by simultaneous treatment with HC1 and H2S. 

To further exploit the potential usefiilness of this new family of clusters, monoadduct 54 was saponified into 55 (0.05 M NaOH, quant) and condensed to L-lysine methyl ester using 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline (EEDQ) to give extended dimer 56 in 50 % yield together with monoadduct in 15 % yield [75]. Additionally, tert-butyl thioethers 52 could be transformed into thiols by a two step process involving 2-nitrobenzenesulfenyl chloride (2-N02-PhSCl, HOAc, r.t, 3h, 84%) followed by disulfide reduction with 2-mercaptoethanol (60%). Curiously, attempts to directly obtain these thiolated telomers by reaction with thioacetic acid f ed. These telomers were slightly better ligands then lactose in inhibition of binding of peanut lectin to a polymeric lactoside [76]. 

The synthesis of the second building block [62] for meropenem starts from trans-hydroxyproline. First, the amino acid is protected on both, the amino and the carboxyl group. By reaction with thioacetic acid m a Mitsunobu esterification, the thiol ftmction is introduced, and the carboxyl group is then selectively deprotected with trifluoroacetic add. The dimethylamino-group is introduced with the aid of isopropyl chloroformate, and the thiol acetate is finally hydrolysed with aqueous sodium hydroxide. 

Synthesis of Acetyl Ethyl Disulfides. S- Ethyl ethanethiosulfinate can be rapidly converted to acetyl ethyl disulfide In moderate yield by reaction with thioacetic acid (eq 10). Advantageously, the liberated ethylsulfenic acid can regenerate the thiosulfinate via dehydration. Acetyl ethyl disulfide is a key intermediate for the synthesis of the ethyl hydrodisulfides, which can be prepared by acid catalyzed hydrolysis. 

A topical relation between the esteratic and anionic sites is implicit in any consideration of enzyme action in which the two sites participate. It seems reasonable to assume that the two sites are spaced to accommodate choline esters. The proximity of the sites is indicated by the ability of prostigmine to inhibit the reaction with thioacetic acid, which does not involve interaction with the anionic site. The necessity for binding acetylcholine at both sites for efficient catalysis has been used to explain inhibition by excess substrate. When high concentrations of acetylcholine are present, it is possible for one molecule to interact with the anionic site of the enzyme, while a second molecule associates with the... 

The preparation of quinazoline-2(and 4)-thiones follows those of the corresponding pyrimidines (67HC(24-1)270) but there is at least one special primary synthesis for quinazoline-4(3H)-thiones, illustrated by the reaction of o-aminobenzonitrile with thioacetic acid at 110 °C to give 2-methylquinazoline-4(3H)-thione in 90% yield (53JA675). 

The parent hexathiaadamantane (185) is obtained preparatively when a solution of formic acid and hydrochloric acid in nitrobenzene is allowed to stand for several weeks in a hydrogen sulfide atmosphere the product which separated is almost insoluble in all common solvents and purification presents a problem. Only large volumes of dimethyl sulfoxide at reflux serve for recrystallization.224 The reaction of thioacetic acid with formic acid in the presence of zinc chloride gives tetramethyl-(186), monomethyl-, dimethyl-and trimethylhexathiaadamantane derivatives (187).225 Other variations include the reaction of thioacetic acid with a /i-diketone,226 and the use of boron trifluoride227 or aluminum chloride as a catalyst.228... 

Glycosyl halides (7a-e) were stereoselectively transformed into l,2-tra s-thio-glycoses by i) (8a-d, 8j) a two-step procedure via the pseudothiourea derivatives [9,10a] the substitution of halide by thiourea is mostly a S l-type reaction since acetylated 1-thio-a-D-mannose (8b) was obtained from acetobromoman-nose (7b) [9cj ii) (8e-i) using thiolates in protic and aprotic solvents [10], or under phase transfer catalysis conditions [11]. Another approach involved the reaction of thioacetic acid with 1,2-trans-per-O-acetylated glycoses catalyzed with zirconium chloride [12]. The 1,2-trans-peracetylated 1-thioglycoses (8e-h) were obtained in high yield. No anomerized products could be detected in these reactions (Fig. 1). 

Cyano-l,2,5-selenadiazole-3-carbothioamide 237 was obtained by the reaction of 3,4-dicyano-1,2,5-sclcnadiazole 81 with thioacetic acid in benzene in 73% yield (Equation 31) <1998PCA9021>. 

Effect of Wood Moisture. It has been recommended that for acetylation with acetic anhydride, the moisture content of wood should be about 2% as excess moisture is likely to react with acetic anhydride and produce acetic acid (37). Goldstein et al. (28) observed that raising the moisture to 22% considerably slowed the reaction and each 1 percent of moisture in wood would lead to hydrolysis of about 5.7% acetic anhydride. Low moisture contents are not possible to attain in commercial treatment of wood. With ketene gas it has been possible to acetylate wood with as high as 20% moisture content with WPG about 25% (40). Thioacetic acid is only partially stable in cold water and dissociates at higher temperatures. The presence of moisture in wood could thus be critical in treatments with thioacetic acid also. Results of mango treated at 5 different moisture levels are depicted in Figure 3. As may be seen a moisture content up to 7.5% has no adverse effect on WPG. At 10% moisture content the WPG decreased to 4.6. With further increase in moisture, there was a gradual decrease in WPG attained. 

Figure 3. Effect of different moisture levels on vapor-phase acetylation of wood with thioacetic acid. Reaction time is 3 h.

D d During chemical modification of wood with thioacetic acid, the only by-product formed is H2S gas. This easily escapes from wood favoring a forward reaction. The liberated H2S is recycled to produce thioacetic acid, making the process a closed circuit one. Since there is no crosslinking or polymerization of the reagent, acetylation level can be directly gauged from the WPG. 

Displacement reactions of 3-chloro-l,2-benzisothiazole (26) have already been mentioned in Section II,A, 8.18,19 22 24 In some cases this displacement is accompanied by a rearrangement. Boshagen has shown that treatment of the above-mentioned compound (26) with thioacetic acid yields an A-acyl-3H-l,2-benzodithiole (39).31 This rearrangement is analogous to that described in Section II, C, 2 above. 

In the first redox process (Equation 1), instead of focusing on the iodine itself, the formation of the by-product, that is, HI, is scrutinized because an efficient thiol oxidation depends on HI removal by a base, or its dissolution in a biphasic reaction mixture. Thus, in a reaction monitored by H NMR, 1,3-propanethiol (1 mmol) was quantitatively oxidized to dithiolane 2 with iodine (0.5 mmol) in the presence of 2-methy 1-2-butene (1 mmol), which was completely converted into 2-iodo-2-methylbutane by HI formed in situ. In this case, as well as with thioacetic acid, the same alkene was completely converted by HI to 2-iodo-2-methylbutane, while in an absence of the butene derivative the corresponding disulfides were not detected. 

In the presence of hydrogen chloride, a-acetylenic ketones react with thioacetic acid to give a monothio-)S-diketone which is converted to a 1,2-dithiolium ion by phosphorus pentasulfide or hydrogen sulfide. These reactions, which involve some sort of oxidation, are discussed in the next paragraph. 

Formation of a stable hydro complex with thioacetic acid is particularly interesting, since the reaction with formic or acetic acids, which have similar acidities, leads to an equilibrium in which the hydro complex reductively eliminates in the absence of excess acid (279). 

Further support for the HS AB-based rationalization comes also from later studies demonstrating that making sulfur harder (5 -alkyl to S-acetyl) dramatically alters regioselectivity and leads to 2,3-unsaturated products [176,177]. In the reaction from 3,4-di-O-acetyl-L-rhamnal 87 with thioacetic acid or potassium thioacetate in the presence of BF3 -Et20, only products substituted at C-1 88 and 89 were isolated (O Scheme 30) [177]. 

Very successful has been the aldolase-catalyzed aldol reaction as exemplified inO Scheme 14 [97]. The required (R)-3-thioglyceraldehyde (20) is obtained from regioselective epoxide ring opening of (5)-glycidaldehyde diethyl acetal with thioacetic acid and its potassium salt. Con-... 

---