Catalytic CH Bond Addition of Pyridines to Allenes by a Rare‐Earth Catalyst

Abstract

The catalytic C-H addition of pyridines to allenes has been achieved for the first time by using a half-sandwich scandium catalyst, thus constituting a straightforward and atom-economical route for the synthesis of alkenylated pyridine derivatives. The reaction proceeded regio- and stereoselectively, affording a new family of alkenylated pyridine compounds which are otherwise difficult to synthesize. A cationic Sc-η(2) -pyridyl species was isolated and confirmed to be a key catalyst species in this transformation.

Diastereoselective Cyclization of 1,5‐Dienes with the C−H Bond of Pyridine Catalyzed by a Cationic Mono(phosphinoamide) Alkyl Scandium Complex

“…Pyridine moieties are important components in a large number of natural products, pharmaceuticals, ligands, and functional materials. The C−H alkylation of pyridines with alkenes has received much recent attention as an atom‐efficient route for the synthesis of alkylated pyridine derivatives ,,. At first, the reaction of 1,5‐hexadiene ( 3 a ) with 2‐picoline ( 4 a ) was examined as a model reaction (Table ).…”

“…A possible mechanism for the cis ‐selective cyclization of 3 a with the ortho ‐C(sp 2 )−H bond of 4 a catalyzed by the 2 a ‐Sc/B(C 6 F 5 ) 3 combination is proposed in Scheme . Coordination of the nitrogen atom of 4 a to the scandium center in cationic species A , generated in situ from the reaction of 2 a ‐Sc with B(C 6 F 5 ) 3 , promotes deprotonation of the ortho ‐C(sp 2 )−H bond of 4 a by the alkyl scandium species to give pyridyl intermediate B ,,. Compound 3 a approaches the scandium site from the 2,6‐diisopropylphenyl group side of intermediate B to avoid unfavorable steric interactions from the coordinated aminobenzyl unit of the counteranion, and insertion of a C=C bond of 3 a into the scandium–pyridyl bond in a 2,1‐fashion diastereoselectively gives intermediate C (favored) or C′ (disfavored) .…”

Mechanistic Insights into Rhenium‐Catalyzed Regioselective C‐Alkenylation of Phenols with Internal Alkynes

“…Both isolated 4 and [Re 2 (CO) 10 ] catalyzed this addition reaction. The central carbon atom of the accumulated double bond of the allene was selectively attacked by the aromatic ring, which was accompanied by the addition of a hydrogen atom to the terminal carbon atom . Thus, the substitution pattern of the resultant alkenylated products 5 was opposite to that of 1 obtained from the addition reaction with alkynes (Figure ).…”

Nagoya‐Goldmedaille: S. L. Schreiber / Nagoya‐Silbermedaille: Z. Hou / Kyoto‐Preis (Advanced Technology): K. Kunitake / François‐Gault‐Vorlesung: J. Sauer

“…Er befasst sich mit der Entwicklung von Katalysatoren, Reaktionen und funktionellen Materialien. In Chemistry—An Asian Journal hat er die C‐H‐Carboxylierung aromatischer Verbindungen2a und in Chemistry—A European Journal die katalytische C‐H‐Addition von Pyridinen an Allene2b vorgestellt. Hou war Gründungsmitglied des International Advisory Board von ChemPlusChem (2012–2015).…”