Substitution of Hydroxyl Groups with Alkynyl Moieties Using Alkynylboron Dihalides: An Efficient Approach to Secondary Alkylacetylene Derivatives

Site-Selective Csp3-Csp/Csp3-Csp2 Cross-Coupling Reactions Using Frustrated Lewis Pairs

The donor-acceptor ability of frustrated Lewis pairs (FLPs) has led to widespread applications in organic synthesis. Single electron transfer from a donor Lewis base to an acceptor Lewis acid can generate a frustrated radical pair (FRP) depending on the substrate and energy required (thermal or photochemical) to promote an FLP into an FRP system. Herein, we report the Csp3-Csp cross-coupling reaction of aryl esters with terminal alkynes using the B(C6F5)3/Mes3P FLP. Significantly, when the 1-ethynyl-4-vinylbenzene substrate was employed, the exclusive formation of Csp3-Csp cross-coupled products was observed. However, when 1-ethynyl-2-vinylbenzene was employed, solvent-dependent site-selective Csp3-Csp or Csp3-Csp2 cross-coupling resulted. The nature of these reaction pathways and their selectivity has been investigated by extensive electron paramagnetic resonance (EPR) studies, kinetic studies, and density functional theory (DFT) calculations both to elucidate the mechanism of these coupling reactions and to explain the solvent-dependent site selectivity.

Lewis base directed cycloaddition reactions of 2-pyrones and alkynylaluminum reagents

In situ generated alkynylaluminum reagents have been utilized in a [4 + 2] cycloaddition with 2-pyrones bearing a Lewis basic donor. The reactions proceed at or below room temperature and with complete regiocontrol. This one-pot method affords diversely substituted aromatic compounds under very mild conditions.

Pd-catalyzed three-component coupling of N-tosylhydrazone, terminal alkyne, and aryl halide

A Pd-catalyzed three-component reaction of N-tosylhydrazone, terminal alkyne, and aryl halide follows a mechanism involving a sequence of Pd carbene migratory insertion-transmetalation-reductive elimination, leading to the formation of one sp(2)-sp(3) C-C bond and one sp-sp(3) C-C bond.

Enantioselective nickel-catalyzed cross-coupling reactions of trialkynylindium reagents with racemic secondary benzyl bromides

The first enantioselective sp-sp3 cross-coupling reaction between alkynyl organometals and racemic benzyl bromides is reported. The coupling is performed at room temperature by using NiBr2diglyme and (S)-(iPr)-Pybox as the catalytic system and trialkynylindium reagents as nucleophiles. The reaction is stereoconvergent, both enantiomers of the racemic benzyl bromide are converted into one enantiomer of the product, and stereospecific. The reaction takes place efficiently in good yields and with high atom economy, as the triorganoindium reagents transfer the three organic groups attached to indium (only 40 mol % of R3In is used).

Generation of Cations from Alkoxides: Allylation of Propargyl Alcohols

The reaction of alkoxides with boron trichloride results in the generation of cations in the absence of Brønsted acids. The absence of a Brønsted acid can make a difference in subsequent transformations such as allylation reactions.