Biomimetic transamination of the commercially available ethyl 2-methyl-3-keto-4,4,4-trifluorobutyrate (4) with benzylamine was shown to provide a simple access to the 2-methyl-3-amino-4,4,4-trifluorobutanoic acids, a hitherto unknown biologically relevant β-amino acid. In sharp contrast to the α-unsubstituted β-keto carboxylic esters the transamination of α-methyl β-keto carboxylic ester 4 proceeds under mild reaction conditions, presumably, due to relative instability of the intermediate (Z)-enamine 6. Diastereoselectivity of the process was found to be controlled by the nature of the base-catalyst allowing for a stereodivergent preparation of (2R*,3S*)-8a and (2R*,3R*)-8b diastereomers as dominant reaction products. Preparation of all four diastereo- and enantiomerically pure optical isomers of the 2-methyl-3-amino-4,4,4-trifluorobutanoic acid was effectively accomplished by penicillin acylase-catalyzed resolution of the corresponding diastereomerically pure N-phenylacetyl derivatives. The whole process, a stereocontrolled chemoenzymatic approach, including the diastereoselective base-catalyzed [1,3]-proton shift reaction and the enantioselective penicillin acylase-catalyzed resolution, employs a simple set of reactions, inexpensive reagents, and mild reaction conditions, that would render it methodologically useful for preparing biologically interesting α,β-disubstituted fluorinated β-amino acids.

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ChemInform Abstract In the presence of BF3 the reaction between the difluoroiodotrihydropolyfluoroalkanes (I) and benzene (II) affords the title compounds (III). Their perfluoro analogues are known to be strong perfluoroalkylating agents. For a comparison, the alkylating properties of the title compounds (III) with a methylene bridge between the aryliodonium moiety and the polyfluoroalkyl group are investigated. In the reaction of (IIIa) with p-chlorothiophenol (IV) the perfluoroalkyl group adds to the sulfur atom to give the product (V). The reaction with pyridine (VI) proceeds via addition of the polyfluoroalkyl group to the nitrogen atoms to give the quaternary pyridinium salt (VII). In the reaction of (IIIb) with N,N-dimethylaniline (VIII) the main product is the quaternary salt (IX) accompanied by the p-polyfluoroalkyl derivative (X).

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