Synthesis of β-Hydroxy-α,α-difluorosulfonamides from Carbanions of Difluoromethanesulfonamides.

The synthesis of β-hydroxy-α,α-difluorosulfonamides was achieved by reacting difluoromethanesulfonamides with KHMDS in the presence of an aldehyde or ketone. The reaction exhibited a dramatic counterion effect with KHMDS or NaHMDS usually giving excellent yields in minutes, while lithium bases gave little or no product. Excellent yields and high diastereomeric ratios were achieved with Nα-benzyl-Nα-phenylfluorenyl (PhF)-protected chiral amino aldehydes derived from amino acids. Following deprotection, a β-hydroxy-α,α-sulfonamide reacted under peptide coupling and Mitsunobu conditions to furnish a peptidomimetic in an excellent overall yield.