Reversible 1,4‐Insertion of Pyridine Into a Highly Polar Metal–Carbon Bond: Effect of the Second Metal

摘要: Dihydropyridines (DHPs) serve as selective reducing agents, are useful building blocks in organic chemistry, and represent an important class of pharmacologically active compounds. Transition-metal catalyzed 1,4-selective hydrosilylations silaborations pyridine have recently been reported two new methods for the synthesis DHPs. Remarkably, hydrosilylation was found to be reversible. In general, phenomenon reversibility has recognized few insertion reactions organotransition metal complexes. Some these processes turned into applications such dynamic polymerizations. contrast, reversible unusual polar organometallic compounds Group 1 2 metals. To best our knowledge, metal–carbon bonds not studied detail heavy elements Groups 2. We interested reaction with allyl reagents give N-metalated DHPs a one-step reaction. report here potassium– carbon bond synergetic stabilization product by divalent The instantaneous allylpotassium THF at ambient temperature exclusively gave 1,4-insertion (Scheme 1). Side products due 1,2-insertion, deprotonative metalations, or coupling were observed. exposure 100fold excess [D5]pyridine resulted rapid exchange C5H5N core C5D5N equilibrium observed H NMR spectroscopy. [Li ACHTUNGTRENNUNG(C3H5)ACHTUNGTRENNUNG(PMDTA)] [Na ACHTUNGTRENNUNG(C3H5)] showed similar reactivity patterns (for details see Supporting Information). most likely proceeds via elimination from form back starting material 1, which then undergoes deuterated pyridine. Rearomatization entropy could driving forces potassium assisted Reactions main group organometallics relatively well studied: 1,2-selectivity (M=Li, Al), 1,4-selectivity (M=Mg, Ca), mixtures thereof Sn) reported. However, is unprecedented involving highly reagents. Compound isolated characterized, but stable pyridine, irrespective presence neutral chelating ligands. investigate more detail, we sought way stabilizing compound while preserving its striking characteristic reversibility. Recently, alkali zincates established powerful tools synthesis, they can combine high their organoalkali component selectivity organozinc component. When [K([18]c-6)] [Zn ACHTUNGTRENNUNG(h1-C3H5)3] (3 ; [18]c-6= [18]crown-6) treated one equivalent [18]c-6 2), dianionic tetrakis ACHTUNGTRENNUNG(amido)zincate 4 obtained quantitative yield. This contrast [a] Dipl.-Chem. C. Lichtenberg, Dr. T. P. Spaniol, Prof. J. Okuda Institut f r Anorganische Chemie RWTH Aachen University Landoltweg 52056 (Germany) Fax: (+49)241-80-92644 E-mail : jun.okuda@ac.rwth-aachen.de [b] L. Perrin, Maron Universit de Toulouse et CNRS, INSA, UPS, CNRS UMR 5215 LPCNO 135 avenue Rangueil, 31077 (France) (+33)561-559-697 Laurent.maron@irsamc.ups-tlse.fr information this article available on WWW under http://dx.doi.org/10.1002/chem.201200808. Scheme 1. Reaction [D5]pyridine, exchanged rapidly [D5]-2.