ABSTRACT
Lewis acids such as Cu(OTf)(2), Zn(OTf)(2), Yb(OTf)(3) and Nd(OTf)(3) catalyze the aza-ene reaction of alkenes with azodicarboxylates, giving the allylic amination adducts. The use of bis(2,2,2-trichloroethyl)azodicarboxylate as the amination reagent and Cu(OTf)(2) and Yb(OTf)(3) as the catalysts gave the aza-ene reaction of different alkenes, leading to the corresponding allyl amines in high yields. Chiral copper complexes prepared from Cu(OTf)(2) and chiral bisoxazoline ligands were found to catalyze the enantioselective aza-ene reaction of azodicarboxylates with alkenes and the hetero-Diels-Alder reaction with cyclopentadiene, giving the corresponding aza-ene- and hetero-Diels-Alder adducts, respectively, in good yields and moderate enantioselectivities.
ABSTRACT
The development of a practical one-pot catalytic enantioselective procedure for the synthesis of non-natural aromatic and heteroaromatic alpha-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-alpha-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 alpha-amino acids are demonstrated. The coordination of the N-alkoxycarbonyl alpha-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.
