title: Iridium-catalyzed [2+2+2] cycloaddition of α,ω-diynes with isocyanates.
abstract: [Ir(cod)Cl](2)/BINAP was found to be an efficient catalyst for the [2+2+2] cycloaddition of α,ω-diynes with isocyanates to give 2-pyridones. A wide range of isocyanates can be used for this reaction. Both aliphatic and aromatic isocyanates smoothly reacted with α,ω-diynes to give 2-pyridones in high yields. Aliphatic isocyanates were more reactive than aromatic isocyanates. For aromatic isocyanates, the electronic properties of the substituents affected the reactivity: electron-donating substituents enhanced the reaction. The reaction of unsymmetrical α,ω-diynes possessing two different internal alkyne moieties with isocyanates was regiospecific and gave a single product. This regioselectivity could be explained by the reaction of iridacyclopentadiene with a nitrogen-carbon double bond. The regioselectivity of the reaction of malonate-derived diyne was controlled by a steric effect, while that of the reaction of ester-tethered diyne was controlled by an electronic effect. [Ir(cod)Cl](2)/chiral diphosphine catalyst could be used for the enantioselective synthesis of C-N axially chiral 2-pyridone. The reaction of diyne 1a with o-methoxyphenyl isocyanate (7a) gave C-N axially chiral 2-pyridone (R)-8aa in 78% yield with 94% ee.
authors.affiliation: Department of Chemistry and Biological Science, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo, Sagamihara, Kanagawa 252-5258, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Onodera
authors.forename: Mari
authors.initials: M
authors.lastname: Suto
authors.forename: Ryo
authors.initials: R
authors.lastname: Takeuchi