Phenyl thiopropionate

Simple alkyl or aryl thioesters are commonly assayed as substrates of hydrolases, witness the hydrolysis of phenyl thioesters by horse serum carbox-ylesterase [150], For most substrates investigated, e.g., phenyl thioacetate, phenyl thiopropionate, and phenyl thiobutyrate (7.66, R = Me, Et, and Bu, respectively), kcat values were found, which were a few times larger than those of corresponding nitrophenyl esters, whereas the affinities were lower by approximately one order of magnitude. Methyl and phenyl esters of various linear thioacids were also found to be good substrates of mammalian liver carboxylesterases and serum cholinesterases [151]. 

Aldol condensations with phenyl thiopropionate (2). Reaction of 2 with 1 and a tertiary amine at -7 ° results in a 70 30 mixture of (Z)- and (E)-enolates, whereas reaction at 25° furnishes an 18 82 mixture of these enolatcs. However, both cnolatcs react with aldehydes with high. wn-diastercoselectivity. 

Asymmetric Aldol Reactions. Reaction of (1) with Boron Tribromide in CH2CI2 affords, after removal of solvent and HBr, a complex (5) useful for the preparation of chiral enolates (eq 5). Complex (5) is moisture sensitive and is generally prepared immediately before use. For propionate derivatives, either syn or, less selectively, anti aldol adducts may be obtained by selection of the appropriate ester derivative and conditions. Thus reaction of f-butyl propionate with (5) and triethylamine produces the corresponding E 0) enolate, leading to formation of anti aldol adducts upon addition to an aldehyde (eq 6). Selectivities may be enhanced by substitution of the t-butyl ester with the (+)-menthyl ester. Conversely, reaction of 5-phenyl thiopropionate with (5) and Diisopropylethylamine affords the corresponding Z(0) enolates and syn aldol products (eq 7). ... 

Whereas carboxylic esters had been considered to be inert under the conditions of boron enolate formation by enolization [2c], Corey s group elaborated protocols that allowed for the generation of boron enolates from esters. Thus, trans-boron enolates 100 result from simple carboxylic esters by deprotonation, while 5-phenyl thiopropionate formed cis-enolate 101 - in accordance with Masamune s observation. In both cases, the C2-symmetric diazaborolidine 99 served as the Lewis acid for enolization (Scheme 2.28) [112]. The stereochemical divergence of ester and thioester has been rationalized by postulating an E2-type elimination mechanism starting from the complex 102 that loses bromide in a... 

In addition to phenylacetonitrile and fluorene, various active methylene compounds such as indene, propiophenone, phenyl propionate, benzyl phenylacetate afforded the corresponding carboxylated products by the carboxylation reaction with La(0 Pr)3-Ph-N=C=0-C02 system. Of fundamental and practical importance is that S-benzyl thiopropionate was effectively carboxylated into a thioester of 2-methylmalonate in a good yield, since this reaction is related to the biological carboxylation of propionyl coenzyme A with a biotin enzyme. Other thioesters were also carboxylated similarly, where successful examples were thioesters of phenylacetic, acetic, and isovaleric acids carrying active methylene and methyne groups, respectively. 

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