Diethyl amino sulfur trifluoride

As another example, a continuous two-step liquid phase process was developed involving the geminal difhiorination of a 17-keto steroid using diethyl amino sulfur trifluoride (DAST) and subsequent quenching in alkaline solution to consume the excess reactants [50]. 

The use of fluorine in molecules of pharmacological interest is well known and there has been widespread research into methodologies for the introduction of this atom. Within the discovery synthesis of maraviroc, the initial preparation required the use of diethyl amino sulfur trifluoride (DAST), which is commercially available but does require careful handling due its well known thermal instability. Initial use of DAST for the fluorination of the ketone 19 gave an inseparable 1 1 mixture of the required difluoro compound 20 and the vinyl fluoride 21. The formation of vinyl fluoride co-products from the treatment of ketones with DAST is known in the literature and is difficult to control. 

The main drawback in the catalytic hydrogenolysis of Z-protected peptide derivatives is caused by the presence of sulfur-containing amino acid residues (Cys, Pen, or Met) due to catalyst poisoning. Attempts to overcome these restrictions by addition of either tertiary basesf or boron trifluoride-diethyl ether complext to the hydrogenation mixture were of limited usefulness. More efficient appears to be the use of liquid ammonia (at —33°C) as the solvent to prevent poisoning of the Pd/C catalyst.f °l... 

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