Aminosulfuric acid ester

Fig. 4.29. Dehydration of an alcohol with the Burgess reagent (which in turn is prepared from 0=C=N-S02-CI by (1) addition of methanol and (2) reaction and subsequent deprotonation with triethy-lamine). The aminosulfuric acid ester intermediate decomposes via a cyclic transition state (syn-elimination).

Fig. 4.25. Dehydration of an alcohol with the Burgess reagent. The aminosulfuric acid ester intermediate decomposes via a cyclic transition state (iyn-elimination).

Wipf and co-workers developed an efficient one-pot process to prepare a variety of highly functionalized 2-substituted 4-oxazolecarboxylic acid esters 39. The starting (3-hydroxyamides 1588 were cyclodehydrated using Deoxo-fluor (bis(2-methoxyethyl)aminosulfur trifluoride) or DAST (diethylaminosulfur trifluoride) to afford intermediate oxazolines 38, which were oxidized in situ with B1CCI3/ DBU to afford 39 (Scheme 1.404). DAST was found to be preferable with serine-derived p-hydroxyamides, whereas Deoxo-fluor was more useful for threonine derived p-hydroxyamides. 

The reaction of ketones with diethylaminosulfur trifluoride or related aminosulfur trifluorides in the presence of fuming sulfuric acid affords vinyl fluorides (see Vol. FlOa, p415). Certain fS-oxo esters and pcntanc-2.4-dione react with diethylaminosulfur trifliioride to give a,/Fdifluoro-a,/i-unsaturated esters and 3,4-difluoropent-3-cn-2-one, respectively. In the reaction of y-oxocarboxylic acids with diethylaminosulfur trifluoride cyclization leads to y-fluorobutyrolactones. ... 

These reactions are most important for the preparation of acyl fluorides. Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution or with liquid HF at —10° C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids.Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with diethyl-aminosulfur trifluoride (DAST). Carboxylic esters and anhydrides can be... 

Carboxylic acid 125 was coupled with ethanolamine or L-serine methyl ester hydrochloride in the presence of EDCI, HOBt, and EtsN to afford the corresponding p-hydroxy amides, which were cyclized using bis(2-methoxyethyl)aminosulfur trifluoride (Deoxo-Fluor) to afford oxazolines (149 and 150, Scheme 24) [56, 57]. Oxazoline 150 was converted to oxazole 151 in 80% yield by treatment with bromotrichloromethane and DBU, conditions which did not lead to epimerization at C-8 [57], A variety of oxadiazoles (152-158) have been produced in 10-56% yield by treating carboxylic acid 125 with appropriate amidoximes in the presence of EDCI and HOBt followed by heating in toluene (Scheme 24) [44, 57, 58]. These conditions led to some epimerization at C-8, necessitating purification by HPLC. Carboxylic acid 125 was treated with either (2-hydroxybenzyl)triphenyl- or (2-thiobenzyl)triphenyl phosphonium bromide in the presence of CDMT and EtsN to afford the benzofuran (159) and benzothiophene (160) products in 26 and 35% yield, respectively (Scheme 24) [58]. 

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