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A nickel/N‐heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B2(neop)2 (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron‐deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni‐catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4‐(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans‐[Ni(ICy)2(4‐CF3‐C6H4){(SO)‐4‐MeO‐C6H4}] 4. For complex 5, the isomer trans‐[Ni(ICy)2(C6H5)(OSC6H5)] 5‐I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans‐[Ni(ICy)2(C6H5)(OSC6H5)] 5‐I is in equilibrium with the S‐bonded isomer trans‐[Ni(ICy)2(C6H5)(SOC6H5)] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2‐TZVP‐level of theory) and connected via a transition state trans‐[Ni(ICy)2(C6H5)(η2‐{SO}‐C6H5)], which lies only 10.8 kcal/mol above 5. [ABSTRACT FROM AUTHOR]

Pd‐catalyzed spiroannulation of bromophenylnaphthalenols with acetylenes to achieve asymmetric dearomatization is a powerful way to construct chiral spiro‐compounds. DFT calculations with the M06 functional have been performed to reveal the mechanism and enantioselectivity of this reaction. After reversible oxidative addition of aryl bromide to Pd(0), acetylene insertion into the Pd−C(aryl) bond is considered to be the rate‐ and enantioselectivity determining step. Subsequent deprotonation and reductive elimination then give the spiroannulation product. The overlay and noncovalent interaction analysis of the critical transition states were used to reveal the origin of the enantioselectivity for this reaction. We found that the axial chirality of the naphthol moiety affects the relative free energies of the corresponding transition states, whereas the enantioselectivity is controlled by the steric repulsion between the naphthol moiety and the ligand. [ABSTRACT FROM AUTHOR]