Palladium-Catalyzed Intramolecular Reactions of (E)-2,2-Disubstituted 1-Alkenyldimethylalanes with Aryl Triflates

Abstract

A full account of the Pd-catalyzed intramolecular reactions of (E)-2,2-disubstituted 1-alkenyldimethylalanes with aryl triflates as an entry into polycarbocyclic structures displaying an ethyl−methyl-substituted all-carbon benzylic quaternary center is herein presented. It was found that the efficiency of the Pd-catalyzed carbon−carbon bond forming process is highly affected by the structure of the starting material, including tether length and aryl substitution pattern; substituting the position ortho to the triflate is mandatory to obtain a good yield of the carbocycle. Moreover, the formation of 1-ethyl-1-methylindanes is facile in comparison to the case for the analogous tetrahydronaphthalenes, for which the competing methyl cross-coupling reaction is equally competent. It was established through labeling studies that the carbon−carbon bond forming events are stereospecific and proceed though the intermediacy of a neopentylic sp3-gem-dimetallic palladio(II) dialkylaluminoalkane species, from which a 1,2-methyl migration from aluminum to carbon occurs. Intramolecular palladium-catalyzed reactions of 1-naphthyl triflates with (E)-2,2-disubstituted 1-alkenyldimethylalanes revealed two competing reaction pathways: arylation with sequential 1,2-alkyl migration from aluminum to carbon and intramolecular 1,2-diarylation, in which the catalytic cycle is terminated by direct arylation of the C(sp3)−Pd(II) bond. Factors such as tether length, additives, solvent polarity, and C−H···Pd interactions between the Pd(II) center and the hydrogen atom at the 8-position all influence not only the pathway taken by the (σ-aryl)palladium(II) complexes but also the subsequent reactivity of the (σ-alkyl)palladium(II) complexes.

Terpyridine–Porphyrin Hetero‐Pacman Compounds

“…The C À Pd (2.015 ), Pd À I (2.673 ), and Pd À P bonds (2.316 and 2.341 ) are in agreement with known structures, for which lengths between 1.99-2.03 for the C À Pd bond, 2.66-2.70 for the PdÀI bond, and 2.31-2.35 for the PdÀP bond can be found. [63][64][65][66] A similar result is observed for the bond angles around the central palladium atom of 6.…”

An Alternative Method for Generating Arynes from ortho-Silylaryl Triflates: Activation by Cesium Carbonate in the Presence of a Crown Ether

“…1 H-NMR yields were determined using 1,1,2,2-tetrachloroethane as an internal standard. The spectra obtained for products 3 [28], 5a [43], 5b-d [44], 5e [45], 5f [46], 5g [47], 7 [28], 9 [28], 11 [28], and 13 [48] were identical to those reported in the corresponding references.…”

Pd-Catalyzed Conjunctive Cross-Coupling between Grignard-Derived Boron “Ate” Complexes and C(sp2) Halides or Triflates: NaOTf as a Grignard Activator and Halide Scavenger

“…Rearranged complex D then releases the conjunctive coupling product E upon reductive elimination. While the metal-induced metallate rearrangement step ( C → D ) finds some precedent in the stoichiometric rearrangement reactions of Pt acetylides described by Wrackmeyer 6 and in Pd-catalyzed reactions of alkenyl alanes studied by Fillion, 7 this elementary transformation has not been used in the catalytic construction of boronic esters. Indeed, in terms of precedent, the catalytic cycle in Scheme 2 is most closely aligned with a reaction studied by Murakami 8 involving alkynylborane "ate" complexes, although Murakami proposes alkene carbopalladation followed by invertive reductive displacement of Pd(II) upon 1,2-metallate rearrangement.…”