Cobalt-Catalyzed Regiodivergent Ring-Opening Dihydroboration of Arylidenecyclopropanes to Access Skipped Diboronates

Ligand-controlled regiodivergent cobalt-catalyzed ring-opening dihydroboration of arylidenecyclopropanes is developed to access synthetically versatile skipped diboronates with catalysts generated in situ from Co(acac)₂ and dpephos or xantphos. A variety of arylidenecyclopropanes reacted with pinacolborane (HBpin) to form the corresponding 1,3- or 1,4-diboronates in high isolated yields and with high regioselectivity. Skipped diboronate products from these reactions can undergo various transformations to allow selective installation of two different functional groups along alkyl chains. Mechanistic studies suggest that these reactions combine cobalt-catalyzed ring-opening hydroboration of arylidenecyclopropanes and hydroboration of homoallylic or allylic boronate intermediates.     

Ligand-Controlled Regiodivergence in Nickel-Catalyzed Vinylcyclopropane Rearrangement

A ligand-controlled regiodivergence in Ni-catalyzed rearrangement of vinylcyclopropanes to 1,4- or 1,5-disubstituted cyclopentenes is reported. The 1,4- or 1,5-disubstituted cyclopentene is selectively obtained depending on the choice of ligands. Detailed kinetic studies and density functional theory calculations on the catalytic cycle revealed that the product selectivity is determined at the reductive elimination step from the six-membered η₁-allyl intermediate.     

Direct Catalytic Asymmetric and Regiodivergent N1- and C3-Allenylic Alkylation of Indoles

Herein we report a Pd-catalyzed asymmetric allenylic alkylation strategy for the direct functionalization of 1H-indoles by employing P-chiral BIBOP-type ligands. The regioselectivity (N1/C3) of this process can be switched efficiently. Using Cs₂CO₃ at elevated temperatures in MeCN, N1-alkylated indoles bearing axial chirality with a stereocenter non-adjacent (β) to the nitrogen are produced in good yields with high enantioselectivity and complete N1-regioselectivity regardless of the electronic properties and substitution patterns of diverse indoles. Using K₂CO₃ at room temperature in CH₂Cl₂, chiral C3-alkylated indoles can also be obtained. Notably, we introduce a new class of tri-substituted allenylic electrophiles that proceeded through different pathways from di-substituted allenylic electrophiles.