Asymmetric synthesis of fluorine-containing amines, amino alcohols, α- and β-amino acids mediated by chiral sulfinyl group

This review article provides a critical overview of several different synthetic approaches developed for asymmetric preparation of fluorine-containing amines, amino alcohols, α- and β-amino acids. The common feature of these methods is the application of sulfinyl group as a chiral auxiliary to control the stereochemical outcome of the reactions under study. In particular, the following general methods are critically discussed: diastereoselective methylene transfer from diazomethane to the carbonyl of β-keto-γ-fluoroalkyl sulfoxides as a general approach for preparation of various α-fluoroalkyl α-sulfinylalkyl oxiranes. The resulting compounds were used as true chiral synthons for their further elaboration via oxidative or reductive desulfurization, to numerous fluorine-containing and biologically relevant amino- and hydroxy-containing derivatives. Another general approaches discussed here are asymmetric additions to CN double bond. One of them is addition of chiral sulfoxide stabilized carbon nucleophiles to fluorine-containing imines, leading to convenient preparation of alpha-fluoroalkyl derivatives of alpha amino acids and amines. Another approach is asymmetric Reformatsky reaction between N-sulfinyl imines and ethyl bromodifluoroacetate allowing operationally convenient preparation of α,α-difluoro-β-amino acids in enantiomerically pure form. Finally, structurally similar but mechanistically different addition reactions of diethyl difluoromethylphosphonate to N-sulfinyl imines, as a general approach to asymmetric synthesis of α,α-difluoro-β-aminophosphonates and phosphonic acids, are discussed. Effect of fluorine on the mechanism and stereochemical outcome of these reactions is discussed in detail and compared, where it is possible, with that of the analogous reactions of fluorine-free substrates.