Electroreductive intramolecular coupling of aromatic imino esters: is four-membered cyclization much more favorable than six-membered cyclization?
[reaction: see text] The electroreduction of an aromatic imino ester prepared from (S)-glutamic acid in the presence of chlorotrimethylsilane and triethylamine afforded a four-membered cyclized product, a mixed ketal of cis-2,4-disubstituted azetidine-3-one, stereospecifically. Calculations for the transition states by the DFT method support the predominant formation of the azetidine. The electroreduction of an aromatic imino ester prepared from (S)-aspartic acid gave almost equal amounts of a diastereomerically pure mixed ketal of cis-2,4-disubstituted azetidine-3-one and a diastereomeric mixture of 2,5-disubstituted pyrollidine-3-one.
Kise
Naoki
N
Department of Biotechnology, Faculty of Engineering, Tottori University, Koyama, Tottori 680-8552, Japan. kise@bio.tottori-u.ac.jp
Hirano
Yuuki
Y
Tanaka
Yoshi
Y
D001224:Aspartic Acid / Q000737:chemistry; D001384:Azetidines / Q000138:chemical synthesis* / Q000737:chemistry; D003500:Cyclization; D004952:Esters; D018698:Glutamic Acid / Q000737:chemistry*; D007097:Imines / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011760:Pyrrolidinones / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D001384:Azetidines; D004952:Esters; D007097:Imines; D011760:Pyrrolidinones; D001224:Aspartic Acid; D018698:Glutamic Acid