Catalytic asymmetric synthesis of bis-armed aromatic amino acid derivatives. Problems related to the synthesis of enantiomerically pure bis-methyl ester of the (S,S)-pyridine-2,6-diyl bis-alanine

(S,S)-Pyridine-2,6-diyl bis-alanines 8 and 9 carrying protecting groups suitable for peptide synthesis have been synthesised Rom 2,6-pyridinedicarbaldehyde by the phosphonoglycine condensation route followed by catalytic by hydrogenation with Rh{(COD)[(R,R)-DIPAMP]}BF4. The alternative route via double Heck coupling of 2,6-dibromopyridine and benzyl Boc-amidoacrylate was unsuccessful although mono-coupling could be achieved. The reasons for this failure are discussed as well as the failure of two mono-armed didehydroamino acid derivatives to undergo hydrogenation with Rh-bisphosphine catalysts. The CuCl2 and RhCl3 complexes of the bis-amino derivative 9 were prepared; a 20% e.e. was achieved in the cyclopropanation of styrene with ethyl diazoacetate using the Cu(II)-complex as a catalyst.