Preparation and nucleophilic substitution of the 2,4,6-triphenylpyridinium salts, diazonium intermediates and N,N-1,2-benzenedisulfonylimides of chiral amino acids

Abstract

Three methods for preparation of D-amino acids by nucleophilic substitution on derivatives of their L-antipodes have been attempted. Nucleophilic substitution on optically active phenylalanine ethyl ester triphenylpyridinium salt yielded partial inverted azide products. The N,N-disulfonylimide intermediate of the same ester was synthesized in high yield and optical purity, but the substitution reaction on this compound was not achieved. Diazotization of amino acid ammonium chlorides and tosylates in solution of sodium azide in aprotic solvents gave optically active chloro and tosyl compounds instead of the intended azide products. Alternative methods to circumvent the problem of the competing ammonium salt counterions during diazotization reactions have been suggested.

Deaminative Arylation of Amino Acid-derived Pyridinium Salts

“…C–N bond fragmentation then gives an alkyl radical, which likely combines with a nickel arene intermediate before undergoing reductive elimination to yield the arylated product. In support of an alkyl radical intermediate, we observed racemization in the cross-coupling of enantioenriched 3a , prepared from l -alanine (Scheme , top) . Also, the addition of TEMPO to the cross-coupling yielded TEMPO-trapped adduct 26 (Scheme , middle).…”