Bromo thioesters

A convenient one-pot procedure for the preparation of a-bromo thioesters from carboxylic acids based on the HVZ reaction was developed by H.-J. Liu and co-workers.The neat carboxylic acid was mixed with 0.4 equivalents of PBrs, the resulting mixture was heated to 100-120 °C in an oil bath and 1.2 equivalents of liquid bromine was added in 1.5h. In the same flask, now containing the a-bromo acyl bromide, the solution of the thiol in dichloromethane was added to give the desired a-bromo thioesters in high yield. 

P-Hydroxy carbonyl compounds. Aldol and Reformatsky reactions involving debrominative enolization of a-bromoketones and a-bromo thioesters with TiCl2-Cu-r-BuCN are readily achieved. Acceptors are limited to aliphatic aldehydes because pinacol formation by aromatic aldehydes predominates under the conditions. 

DC. . ii rmatsky reactions involving i d a-bromo thioesters with > limited to aliphatic aldehydes... 

Cycloalkanones. co-Bromo thioesters and selenoesters give cyclic ketones on... 

Boc amino acid thioesters 7 used in Boc-SPPS are prepared by reaction of Boc amino acid active esters such as the 4-nitrophenyl ester (ONp) or succinimide ester 6 (OSu) with thiols containing a carboxy group that can link to a resin (Scheme 3, Table 2). 1314 Amino acid thioesters 7 can also be prepared by reaction of Boc amino thiol acids 8 with a chloro, bromo, or hydroxy compound that also contains a carboxy group (Scheme 3, Table 2). 1516 ... 

Under strongly basic conditions, o-bromoacetophenones and carbon disulphide react to give a high yield of a benzothiopyranone. 2-Bromo-3-pyridyl ketones react with thioesters to produce a fused thiopyranone ring. 

Smutny. The t-butyl ester was used in order to achieve hydrolysis of (30), which required reaction with trifluoroacetic acid at 0 °C for 4—5 h. Treatment of (30) with warm trifluoroacetic acid for 10 min yielded (31). The reaction of (29) with ethyl a-chloroacetate gave (32). A-Phenyl phenylpropynthioamide (33) reacts in a similar manner with active bromomethylene derivatives, such as bromo-acetonitrile, bromonitromethane, and /j-nitrobenzyl bromide, in the presence of triethylamine to give the thiophen (33a). Instead of enamine thioesters such as (29), 2-aminovinyl thioketones (34) react with a-bromo-ketones in the presence of triethylamine to give 2-acyl-thiophens (35). By the ion-pair extraction method, tetrabutylammonium salts of acetylacetone were allowed to react with carbon disulphide to give (36), which upon reaction with chloroacetone gave a 45% yield of the thiol (37), in addition to a thieno[2,3-A]thiophen derivative. ... 

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