Optically Active Aromatic and Heteroaromatic α-Amino Acids by a One-Pot Catalytic Enantioselective Addition of Aromatic and Heteroaromatic C−H Bonds to α-Imino Esters

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Abstract
The development of a practical one-pot catalytic enantioselective procedure for the synthesis of non-natural aromatic and heteroaromatic α-amino acids is reported. Starting from readily available starting materials and application of a chiral BINAP−Cu(I) catalyst, the optically active products are formed with readily removable N-protecting groups. The scope of the reaction is demonstrated by the addition of substituted furans, thiophenes, pyrroles, and aromatic compounds to N-alkoxycarbonyl-α-imino esters in good yields and with enantioselectivities up to 96% ee for the furans, 93% ee for the thiophenes, and 98% for the aromatic compounds. The protecting groups are readily removed, and various transformations of the aromatic and heteroaromatic α-amino acids are demonstrated. The coordination of the N-alkoxycarbonyl α-imino ester to the chiral BINAP−Cu(I) complex and the enantioselectivity of the catalyst is discussed on the basis of the DFT calculations and X-ray crystallographic data.