Synthesis and Characterization of Highly Conjugated, Chiral Bridging Ligands

This paper describes the synthesis of four chiral derivatives of the electronically highly conjugated
tetra-2-pyridylpyrazine (TPPZ) bridging ligand, which are denoted (R)- and (S)-4,5- and 5,6-pineno-tetra-2-pyridylpyrazine (PTPPZ). Preparation of these ligands was undertaken through the use of
commercially available, enantiomerically pure (1R)- and (1S)-α-pinene, which was functionalized
and subsequently employed in a Kröhnke pyridine synthesis involving a furan-substituted
pyridinium salt to yield a chiral, furan-substituted pyridyl intermediate. Oxidative degradation
and subsequent reduction of this furan led to a chiral, substituted 2-pyridylaldehyde, which
underwent a pyridoin condensation followed by cyclization to produce the final PTPPZ ligands.