Diethylaminosulfur trifluoride DAST

Diethylaminosulfur trifluoride (DAST) reacts with epoxides to give com plex mixtures in which vicinal as difluorides, gemmal difluorides, and bis(2-fluoroalkyl) ethers are the mam components I6 (equations 16 and 17)... 

Table 6b. Fluorination of Secondary Alcohols with Diethylaminosulfur Trifluoride (DAST)...

The transformation of an ester carbonyl group to a difluoromethylene group, which IS usually difficult to perform, can be accomplished by conversion to the thiaesier followed by treatment with diethylaminosulfur trifluoride (DAST). A vanety of ester types react efficiently, although the reaction fails with lactones. Remarkably, trimethylsilylmethyl esters carry through the proeedure with the silyl group intact [13] (equation 17). 

In addition to the perfluoroalkylzinc compounds, the zinc reagent formed from 1,1,1-trifluorotrichloroethane has received considerable attention. This zinc compound was first reported as a stable ether complex [56]. Later, the DMF complex was isolated and the structure was determined by X-ray diffraction and shown to be monomeric [57] (equation 50). This zinc reagent undergoes a variety of functionalization reactions, and some typical examples are illustrated in Table 2 [47, 58, 59, 60, 61] The alcohol products (Table 2) can be converted to AiCF=CXCF3 (X = Cl, F) by further reaction with diethylaminosulfur trifluoride (DAST) and l,8-diazabicyclo[5 4.0]undec-7-ene (DBU) [60]... 

A-Acetyl-9-deoxy-9-fluoroneuraminic acid (591) was prepared by treatment of a protected 6-hydroxyl precursor with A, A-diethylaminosulfur trifluoride (DAST) or through condensation of 2-acetamido-2,6-dideoxy-6-fluoro-D-mannopyranose with potassium di(/ >r/-butyl) oxaloacetate. Compound 591 is a substrate for cytidine monophosphate (CMP)-sialic acid synthetase, giving rise to CMP-5-A-acetyl-9-deoxy-9-fluoroneuraminic acid, which is cytotoxic against tumor cells. 5-A-Acetyl-3-fluoroneuraminic acids 592-594 were prepared through fluorine (or acetyl hypofluorite) addition (in AcOH) to methyl 5-acetamido-4,7,8,9-tetra-0-acetyI-2,6-anhy-dro-2,3,5-trideoxy-D- /ycm>D- a/arto-non-2-enopyranosate. Compound 592 was found to be a potent neuraminidase inhibitor. 

Despite the high utility of glycosyl fluorides as stand-alone glycosyl donors, there has been only one example of a direct dehydrative glycosylation whereby hemiacetal activation proceeds through a glycosyl fluoride intermediate. Hirooka and Koto have detailed the use of diethylaminosulfur trifluoride (DAST) for dehydrative glycosylations with hemiacetal donors (Scheme 3.16) [160]. Treatment of a mixture of hemiacetal 1 and alcohol acceptor (R OH) with DAST 108 (2 equiv) at 0°C provides the... 

Treatment of thioglycosides with /V-bromosuccinimide (NBS) in the presence of diethylaminosulfur trifluoride (DAST) or HF-pyridine complex furnishes glycosyl fluorides.23 These can be activated with AgC104/SnCL in the presence of another... 

Diethylaminosulfur trifluoride (DAST) should be handled using appropriate safety equipment (rubber gloves and goggles). DAST was purchased from Carbolabs, Inc., and used as received. 

The synthesis of the corresponding fluoride 24 posed different, but interesting, problems. The diol 25, on treatment with diethylaminosulfur trifluoride (DAST), gave the required fluoride 26 and thence the epoxide 24 after introduction of the four-carbon aglycon. However, with an excess of DAST, the diol 25 was converted into the fluoro lactoside 27, a rearrangement with some precedent [23,... 

These reactions are most important for the preparation of acyl fluorides.1061 Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution996 or with liquid HF at -10°C.1062 Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids.1063 Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid1064 or with diethylaminosulfur trifluoride (DAST).1065 Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 074, as well as with Ph3PX2 (X = Cl or Br), 066 but this is seldom done. Halide exchange can be carried out in a similar manner. When halide exchange is done, it is always acyl bromides and iodides that are made from chlorides, since chlorides are by far the most readily available.1067... 

M. G. Straatmann and M. J. Welch, Fluorine-18-Iabeled diethylaminosulfur trifluoride (DAST) A fluorine-for-hydroxyl fluorinating agent, J. Nucl. Med. 78 151 (1977). 

A well-stirred solution of 0.09 g l-(2,5-dimethoxy-4-(2-hydroxy-ethyl)phenyl)-2-(2,2,2-trifluoroacetamido)propane in 15 mL CH,C12 was cooled to -78 °C and treated with 0.05 g diethylaminosulfur trifluoride (DAST) added dropwise. The pale yellow reaction solution was stirred an additional 5 min and then brought up to room temperature and stirred for 1 h. There was then added (cautiously) 3 mL H20 followed by additional CH2C12. The phases were separated, the organic phase washed with H20, dried with anhydrous Na.SO, and, after filtering off the drying agent, stripped of solvent under vacuum. There was thus obtained 0.088 g of l-[2,5-dimethoxy-4-(2-fluoroethyl)phenyl]-2-(2,2,2-trifluoro-acetamido)propane as a white solid with a mp of 102-104 °C. 

Diethylaminosulfur trifluoride (DAST, Et2NSF3) a-cleaves cyclic ketoximes to give fluorinated carbonitriles,47 e.g. (27)—> (28). Two mechanisms are proposed, one for substrates with substituents that can stabilize an a-carbocation, and an iminium cation route for ketoximes without such groups. 

The displacement of 3 -hydroxyl group of 270 with fluorine was attempted with diethylaminosulfur trifluoride (DAST) but the reaction resulted in the formation of a nonfluorinated product 101 (Scheme 61) <1997T9357>. 

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