Regiospecific synthesis of 4-fluoro-Δ4,3-keto steroids using caesium fluoroxysulfate

Abstract

The regiospecific synthesis of two A-ring fluorinated steroids is described. Treatment of a 4-trimethylstannyl Δ⁴,3-keto steroid with caesium fluoroxysulfate gave the corresponding fluorinated steroid in good yield; use of the N-fluorodiazabicyclic reagent, Selectfluor, as the fluorine source provides the same compounds in lower yield. The fluorination was found to be sufficiently rapid to be potentially useful in the synthesis of ¹⁸F labelled steroids for PETT applications.