Thioacetal

The carbanions derived from thioacetals, however, are typical -synthons. Most frequently used are 1,3-dithianes and C -silylated thioethers (see p. 33f. D. Seebach, 1969, 1973 B.-T. Grobel, 1974,1977). In these derivatives the proton is removed by butyllithium in THF. 

The synthesis of 11-oxaprostaglandlns from o-glucose uses the typical reactions of gl cofuranose diacetonide outlined on p. 267. Reduction of the hemiacetal group is achieved a thioacetal. The carbon chains are introduced by Wittig reactions on the aldehyde grou] which are liberated by periodate oxidation and laaone reduction (S. Hanessian, 1979 G Lourens, 1975). 

Thioacetyl derivatives (155) are obtained by direct heterocyclization reactions (365. 378, 563) and by a sulfur-oxygen exchange" reaction involving thioacetic acid and A-2-oxazoline-5-one (154) or A-2-thiazoline-5-one (156) (Scheme 81) (365, 378, 379). Ra-Ni reduction of 155 affords the 5-unsubstituted thiazole (379). 

A-2-Oxazoline-5-one (2091 when treated with thioacetic acid yields the corresponding thiazoline-5-one (210) (Scheme 107) (458. 461). These results have been questioned recently (365) however, it appears in the later report that a large excess of thioacetic acid was used instead o-f the stoichiometric amount previously used. 

Phenyl-4-methyl-A-2-thiazoline-5-one (220) treated with excess SOjClj in dichloroethane and the crude product treated with thioacetic acid yields the 4-thioacetyl derivative (221) (Scheme 111) (446). 

The condensation of thioacetic acid with amino acids under drastic conditions provides a useful new synthesis of thiazoles (Scheme 146) (668, 669). Instead of the amino acid, Af-acyl <279) or N-thioacylamino acids (278) are used. 

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... 

Carbanioas derived from the other above mentioned methane derivatives react with alkylboranes, bornic, and boronic esters, providing rich possibihties for the preparation of siagle-carbon iasertion products. Thus 2-aLkyl-l,3,2-dithiaborolanes are converted iato acids or thioacetals by trichloromethyllithium (335). 

The addition of aromatic and aUphatic thiols, RSH and ArSH, and a thioacetic acid to isoprene yields mainly the trans-l,4-adduct (56). The aromatic thiyl radicals, ArS , add almost entirely to the first carbon atom however, aUphatic thiyl radicals, RS, also add to the fourth C atom in significant amounts. 

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

Pharmaceuticals and Agrochemicals. Thioglycohc acid and its esters are useful as a raw material to obtain biologically active molecules. In cephalosporine syntheses, (4-pyridyl)thioacetic acid [10351 -19-8] (65) and trifluoromethane (ethyl) thioglycolate [75-92-9] (66) are used as intermediates. Methyl-3-ainino-2-thiophene carboxylate can be used as intermediate for herbicidal sulfonylureas (67) and various thiophenic stmctures (68). 

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). 

---