Dearomative [2,3] sigmatropic rearrangement of ammonium ylides followed by 1,4-elimination to form α-(ortho-vinylphenyl)amino acid esters.

A base-induced dearomative [2,3] sigmatropic rearrangement of amino acid ester-derived ammonium salts followed by 1,4-elimination produced α-(ortho-vinylphenyl)amino acid esters. The reaction of azetidine-2-carboxylic acid-derived ammonium salt, (1S,2S,1'R)-3b, proceeded with a perfect N-to-C chirality transfer to afford α-(ortho-vinylphenyl)azetidine-2-carboxylic acid ester, (R)-5 (99% ee). On the other hand, the reaction of glycine-derived ammonium salt (R)-6a, which involves an efficient chirality transfer from a chiral benzylic carbon to an α-carbon of an ester carbonyl giving the optically active α-(ortho-vinylphenyl)glycine ester, (R)-8a (85% ee), was demonstrated.

Structural and mechanistic studies of the base-induced Sommelet-Hauser rearrangement of N-α-branched benzylic azetidine-2-carboxylic acid-derived ammonium salts.

The base-induced Sommelet-Hauser rearrangement of N-α-branched benzylic azetidine-2-carboxylic acid ester-derived ammonium salts to obtain α-arylazetidine-2-carboxylic acid esters was investigated. The substrates, two diastereomeric salts (1S,2S,1'S)- and (1R,2R,1'S)-2, showed different reactivities. The rearrangement of (1S,2S,1'S)-2a proceeded with a perfect N-to-C chirality transfer to provide (R)-3a in 74% yield with 99% ee.