Search for: All records

Abstract A kinetic, product, and computational study on the reactions of the cumyloxyl radical (CumO•) with 1,4-dimethyl- and 1,4-diphenylcyclohexanes is reported. The rate constants for hydrogen atom transfer (HAT) from the C–H bonds of these substrates to CumO•, together with the corresponding oxygenation product distributions reveal the role of strain release on reaction site selectivity. Transition structures and activation barriers obtained by DFT calculations are in excellent agreement with the experimental results. Tertiary/secondary ratios of oxygenation products of 0.6, 1.0, and 3.3 were observed, for trans-1,4-dimethyl-, cis-1,4-dimethyl-, and trans-1,4-diphenylcyclohexane, respectively. With cis-1,4-diphenylcyclohexane, exclusive formation of the diastereomeric tertiary alcohol products was observed. Within the two diastereomeric couples, the tertiary equatorial C–H bond in the cis- isomer is ca. 6 and 27 times more reactive, respectively, than the tertiary axial ones, a behavior that reflects the release of 1,3-diaxial strain in the HAT transition state. The tertiary axial C–H bonds of the four substrates show remarkably similar reactivities in spite of the much greater stabilization of the benzyl radicals resulting from HAT from the 1,4-diphenylcyclohexanes. The lack of benzylic acceleration is discussed in the framework of Bernasconi’s ‘principle of nonperfect synchronization’. 

Abstract The transition‐metal‐catalyzed Suzuki‐Miyaura cross‐coupling (SMC) reaction of organoboron nucleophiles with aryl (pseudo)halide electrophiles is a reliable method for carbon‐carbon bond formation. This reaction generally requires the use of an exogenous base to promote transmetalation process, which limits the substrate scope of the reaction due to undesired protodeboronation and functional group incompatibilities. Here, we established a base‐free SMC reaction via a conceptually different electrophilic substitution transmetalation (EST). This transformation is applicable to a wide range of base‐sensitive and sterically hindered organoborons. Key to this advance is the formation of a stable cationic palladium(II) or nickel(II) intermediate via experimental and theoretical investigations. In a broader context, this research further expands the synthetic boundary of cross‐coupling chemistry. 

Group 13 aminoxy complexes, (L)E(TEMPO)₃(TEMPO = 2,2,6,6-tetramethylpiperidine 1-oxyl; L = THF (tetrahydrofuran) or Py (pyridine); E = Al, Ga, In), display ambiphilic reactivity with H₂and function as synthons for the preparation of materials. 

Abstract While enantioenriched alcohols are highly significant in medicinal chemistry, total synthesis, and materials science, the stereoselective synthesis of tertiary alcohols with two adjacent stereocenters remains a formidable challenge. In this study, we present a dual catalysis approach utilizing photoredox and nickel catalysts to enable the unprecedented chemoselective functionalization of tertiary allylic C−H bonds in allyl ethers instead of cleaving the C−O bond. The resulting allyl‐Ni intermediates can undergo coupling with various aldehydes, facilitating a novel enantioconvergent approach to access extensively functionalized homoallylicsec,tert‐vicinal diols frameworks. This protocol exhibits nice tolerance towards functional groups, a broad scope of substrates, excellent diastereo‐ and enantioselectivity (up to 20 : 1 dr, 99 %ee). Mechanistic studies suggested that allyl‐Ni^IIacts as the nucleophilic species in the coupling reaction with carbonyls. 

In silicoexamination of 13P,N-ligated Au(iii) OACs determined the key mechanistic factors governing Au(iii)-mediatedS-arylation. Three complexes were synthesized which exhibited bimolecular coordination rate constants as high as 20 200 M⁻¹s⁻¹.