Palladium-catalyzed cyclization reactions via carbometallation

Frederic Lamaty, Purdue University

Abstract

Treatment of benzyl halides and related electrophiles containing alkene and alkyne groups with a catalytic amount of Pd complexes, such as Pd(PPh$\sb3)\sb4,$ provides the corresponding cyclization products containing five- through seven-membered rings often with retention of the alkene regiochemistry. The reaction of $\omega$-(o-iodoaryl)- and $\omega$-(Z-$\beta$-iodoalkenyl)alkynes with organometals containing Zr, Sn, Al, or B in the presence of a catalytic amount of a palladium-phospine complex, such as Pd(PPh$\sb3)\sb4$, proceeds predominantly via initial cyclic carbopalladation followed by cross coupling, whereas the corresponding reaction of organozincs tends to be dominated by direct cross coupling. The cyclization reaction of alkenylpalladium species containing an $\omega$-gem-disubstituted alkene can give either bicyclo (n.1.0) alkenes or cycloalkenes containing an exocyclic alkene. In those cases where the formation of common rings (5-, 6-, and 6-membered rings) is involved, both reactions proceed via exo-mode cyclic carbopalladation of alkenylpalladium species followed by cyclopropanation. Conformationally rigid cyclopropylcarbinylpalladium species may be converted to vinylcyclopropanes, provided that there is a $\beta$-hydrogen syn coplanar with Pd. If the cyclopropylcarbinylpalladium species are conformationally flexible, their rearrangement to homoallylpalladium species tends to dominate the course of reaction, which then may be followed by dehydropalladation to give apparent endo-mode cyclic carbopalladation with inversion of alkene configuration. Treatment of alkenyl or aryl iodide containing alkyne or alkene and alcohol functionalities with Pd complexes such as Cl$\sb2$Pd(PPh$\sb3)\sb2$ in the presence of CO provides the corresponding cyclized carbonylated products.

Degree

Ph.D.

Advisors

Negishi, Purdue University.

Subject Area

Organic chemistry

COinS