Palladium-catalyzed Tsuji-Trost-type reaction of benzofuran-2-ylmethyl acetates with nucleophiles

The palladium-catalyzed benzylic-like nucleophilic substitution of benzofuran-2-ylmethyl acetate with N, S, O and C soft nucleophiles has been investigated. The success of the reaction is dramatically influenced by the choice of catalytic system: with nitrogen based nucleophiles the reaction works well with Pd2(dba)3/dppf, while with sulfur, oxygen and carbo-nucleophiles [Pd(η3-C3H5)Cl]2/XPhos is more efficient. The regiochemical outcome shows that the nucleophilic substitution occurs only on the benzylic position of the η3-(benzofuryl)methyl complex. The high to excellent yields and the simplicity of the experimental procedure make this protocol a versatile synthetic tool for the preparation of 2-substituted benzo[b]furans.

Tandem Ullmann-Goldberg Cross-Coupling/Cyclopalladation-Reductive Elimination Reactions and Related Sequences Leading to Polyfunctionalized Benzofurans, Indoles, and Phthalanes

On exposure to a combination of Cu[I]- and Pd[0]-based catalysts, compounds such as 1 and 7 engage in tandem Ullmann-Goldberg cross-coupling and cyclopalladation-reductive elimination reactions to give benzofurans such as 8. Related reactions involving hetero-Michael additions of o-halogenated phenols or anilines to propiolates and the Pd[0]-catalyzed cyclization of the resulting conjugates provide, in a one-pot process, alternately functionalized benzofurans, indoles, or phthalanes.

Palladium-catalyzed aerobic (1+2) annulation of Csp3-H bonds with olefin for the synthesis of 3-azabicyclo[3.1.0]hex-2-ene

A novel palladium-catalyzed aerobic (1+2) annulation was developed for the synthesis of 3-azabicyclo[3.1.0]hex-2-ene. The palladation of Csp³-H bonds took place twice at the same position in the whole reaction process. Preliminary mechanistic studies by in situ IR revealed that the second C-H palladation and reductive elimination might be slow steps.

Direct Arylation of Benzo[b]furan and Other Benzo-Fused Heterocycles

The direct arylation of benzo[b]furan, benzo[b]thiophene, and indole has been studied by using aromatic bromides as the aryl source. The protocol employing common reagents and a Pd catalyst has led to the regioselective arylation of these heterocycles at the 2-position. A range of functional groups were tolerated, providing quick access to a variety of arylated benzo-fused heterocycles that would be accessible more elaborately using classical synthetic strategies. This is the first systematic study of the direct arylation of benzo[b]furan.

Scalable, transition-metal-free direct oxime O-arylation: rapid access to O-arylhydroxylamines and substituted benzo[b]furans

O-aryloximes, generated from readily available and inexpensive oximes through transition-metal-free O-arylation, can either be hydrolyzed to O-arylhydroxylamines or conveniently converted to structurally diverse benzo[b]furans through an environmentally benign, one-pot [3,3]-sigmatropic rearrangement/cyclization sequence.

Direct assembly of 3,4-difunctionalized benzofurans and polycyclic benzofurans by phenol dearomatization and palladium-catalyzed domino reaction

A method to directly convert 2-alkynylphenols to 3,4-difunctionalized benzofurans and polycyclic benzofurans was developed. This protocol involves a hypervalent-iodine-mediated oxidative dearomatization to break the aromaticity of 2-alkynylphenols, and a palladium-catalyzed domino reaction to install two functional groups at the C3 and the C4 positions and restore the aromaticity of benzofurans.

Zinc-gold cooperative catalysis for the direct alkynylation of benzofurans

The direct alkynylation of benzofurans was achieved for the first time using the hypervalent iodine reagent 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) based on the cooperative effect between a gold catalyst and a zinc Lewis acid. High selectivity was observed for C2-alkynylation of benzofurans substituted with alkyl, aryl, halogen and ether groups. The reaction was also successful in the case of the more complex drug 8-methoxypsoralen (8-MOP).