Catalytic Electrophilic Alkylation of p‐Quinones through a Redox Chain Reaction

Allylation and benzylation of p ‐quinones was achieved through an unusual redox chain reaction. Mechanistic studies suggest that the existence of trace hydroquinone initiates a redox chain reaction that consists of a Lewis acid catalyzed Friedel–Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. The addition of Hantzsch ester as an initiator improves the efficiency of the reaction.     

Sulfone–Metal Exchange and Alkylation of Sulfonylnitriles

The first general sulfone–metal exchange is described. Treating substituted 2‐pyridylsulfonylacetonitriles with either BuLi or Bu₃MgLi generates metalated nitriles that efficiently intercept a variety of electrophiles to afford quaternary nitriles. The 2‐pyridylsulfone is critical for the sulfone–metal exchange because chelation anchors the organometallic proximal to the electrophilic, tetrasubstituted sulfone to override complex‐induced deprotonation. Alkylating commercial 2‐pyridinesulfonylacetonitrile with mild bases, either K₂CO₃ or DBU, and subsequent sulfone–metal exchange and alkylation rapidly assembles quaternary nitriles by three alkylations, only one of which requires an organometallic reagent.     

Palladium‐Catalyzed Alkylation with Alkyl Halides by C(sp3)−H Activation

Utilizing halogens as traceless directing goups represents an attractive strategy for C−H functionalization. A two C−H alkylation system, initiated by the oxidative addition of organohalides to Pd⁰, has been developed. The first reaction involves an intermolecular alkylation of palladacycles to form C(sp³)−C(sp²) bonds followed by C(sp²)−H activation/cyclization to deliver alkylated benzocyclobutenes as the final products. In the second reaction, two C−C bonds are formed by the reaction of palladacycles with CH₂Br₂, and provides a facile and efficient method for the synthesis of indanes. The alkylated benzocyclobutene products can be transformed into tricyclic hyrocarbons, and the indane derivatives are essential structural motifs in bioactive and odorant molecules.     

Sulfonamide‐Promoted Palladium(II)‐Catalyzed Alkylation of Unactivated Methylene C(sp3)?H Bonds with Alkyl Iodides

The alkylation of unactivated β‐methylene C(sp³) H bonds of α‐amino acid substrates with a broad range of alkyl iodides using Pd(OAc)₂ as the catalyst is described. The addition of NaOCN and 4‐Cl‐C₆H₄SO₂NH₂ was found to be crucial for the success of this transformation. The reaction is compatible with a diverse array of functional groups and proceeds with high diastereoselectivity. Furthermore, various β,β‐hetero‐dialkyl‐ and β‐alkyl‐β‐aryl‐α‐amino acids were prepared by sequential C(sp³) H functionalization of an alanine‐derived substrate, thus providing a versatile strategy for the stereoselective synthesis of unnatural β‐disubstituted α‐amino acids.