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.本论文报道了电子高度共轭的四-2-吡啶基吡嗪（tetra-2-pyridylpyrazine, TPPZ）桥联配体的四种手性衍生物的合成工作，该类衍生物分别记为(R)-、(S)-4,5-及5,6-蒎烯基四-2-吡啶基吡嗪（pineno-tetra-2-pyridylpyrazine, PTPPZ）。本研究以商用对映体纯的(1R)-和(1S)-α-蒎烯为起始原料制备上述配体：先对其进行官能化修饰，随后通过涉及呋喃取代吡啶鎓盐的克罗恩（Kröhnke）吡啶合成反应，得到手性呋喃取代吡啶中间体。对该呋喃中间体进行氧化降解与后续还原，得到手性取代的2-吡啶醛；该醛经吡啶偶姻（pyridoin）缩合反应后再经环化步骤，最终得到目标PTPPZ配体。