Organocatalytic Total Syntheses of (+)- and (–)-Trigonoliimine A

Key words

Michael addition - cinchona alkaloid - trigonoliimine A

Significance

The Zhu group reports an enantio­selective Michael addition of methyl α-aryl-α-isocyanoacetates to vinyl phenylselenone catalyzed by a cinchona-alkaloid derivative. The obtained enantioenriched α-aryl-α-(2′-phenylselenonyl­ethyl)-α-isocyanoacetates are successfully transformed into linear and cyclic quaternary α-amino acids, oxindoles, and pyrrolidinones. A concise total synthesis of (+) and (–)-trigonoliimine A (9 steps, 7.5% and 6.8% overall yield) from the shown Michael adduct was completed via a modified Bischler–Napieralski cyclization.

Comment

α-Isocyanoacetates are well-established glycine templates for the synthesis of racemic α,α-disubstituted α-amino acids. Yet, the ­catalytic enantioselective allylation of α-isocyanoacetates remains underexploited. The reported Michael addition products are converted further without racemization into the corresponding amines and azides. The absolute configuration of the products obtained from the shown cinchona-alkaloid catalyst was determined after derivatization by X-ray analysis to be R.