Thionyl chloride method, acyl chlorides synthesis

Although introduced over 40 years ago, Hurd and Mori s synthesis of 1,2,3-thiadiazoles remains the most widely used for the synthesis of 1,2,3-thiadiazoles. The simplicity of the method has contributed to its popularity. A variety of ketones and aldehydes have been converted into their corresponding hydrazones (tosyl and acyl), and thioamides have been converted into thio-carbazonate esters. The carbonyl derivatives are then treated with thionyl chloride to yield 1,2,3-thiadiazoles in high yields. When one is faced with the task of synthesizing new 1,2,3-thiadiazoles, Hurd and Mori s method should always receive attention. 

N-Acylsaccharins (13) possess a certain potential as acylating agents. They will acylate amines, but will react with water or alcohols only when acid or base is present.167 The method was used to acylate a-amino-penicillanic acid.170 Micheel162-165 has based a peptide (38) synthesis on the acyl transfer from 31 [Z = carbobenzoxy, obtained through reaction with DCC or with pseudosaccharin chloride (6) or with thionyl chloride and imidazole] to amino acids. Pseudosaccharin anhydride 323, lee js thg product of a condensation between 6 and 1, mostly from hydrolysis of 6. Formation of 32 tends to occur in nonprotic solvents with base catalysis, even when practical precautions are taken to exclude moisture. Water and protic solvents seem to shield the anion 19 and prevent attack on 6. 

Carboxyl Activation Synthesis of Esters and Amides from Carboxylic Acids. 4-(Dimethylamino)pyridinium chlorosulfite chloride is more reactive than either thionyl chloride or thionyl chloride/pyridine for carboxyl activation. Aliphatic and aromatic, as well as amino acids (in racemic form), undergo activation (via the acyl halide) and subsequent esterification by reaction with an alcohol at — 20 °C (eq 1). The esterification step requires the addition of a second equivalent of DMAP and this method has been applied to a range of functionalized carboxylic acids. 

The 2,2-linked dimer 48 of 1 was prepared by 2-Uthiation and then oxidation using CuCl2 [32], The 3,3-linked dimer 50 resulted from a combination of 3-bromothieno [3,2-f>]thiophene (19) and 3-trimethylstannylthieno[3,2-6]thiophene (49) [33], Another method for the synthesis of 50 involved a reductive coupling of two molecules of 51, which was prepared from the reaction of 23 with thionyl chloride followed by intramolecular acylation in the presence of AICI3 (Scheme 13) [34],... 

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