Novel molecular scaffolds were developed for introducing nucleophiles into α-, γ-, and α’-positions of the acetylenic tetrads and hexads wherein the triple bond is immobilized by π-bonding to a dicobalthexacarbonyl core. The coordination with a transition metal provided significant advantages by precluding an acetylene-allene rearrangement and facilitating an in situ generation of cationoid species. A wide range of nucleophiles, such as furan, allyl-TMS, methallyl-TMS, 1,3,5-trimethoxybenzene, trimethylsilyl cyanide, and silyl enol ethers can be introduced to competing electrophilic centers with the selectivity being controlled by the stability of the cationoid species and their susceptibility to projecting a reaction center within an allylic triad. Topologically diverse substrates were designed in order to probe relative reactivities of a series of metal-stabilized electrophiles, including 1°, 2°, and 3° propargyl and allyl intermediates that in turn were electronically and sterically altered by alkyl, cycloalkyl, phenyl, 2-furyl, and 2-naphthyl substituents. Novel synthetic protocols allowed for introducing either a given nucleophile to both termini of the acetylenic tetrad (α-Nu1-α’-Nu1; α-Nu2-α’-Nu2), or a pair of select nucleophiles arranged asymmetrically in opposing sequences (α-Nu1-α’-Nu2; α-Nu2-α’-Nu1). Computational data were used for interpreting experimental results, and also for predicting the site-selectivities for novel combinations of substituents that can be introduced into select positions of the acetylenic tetrads and hexads. Overall, quadruple ionic functionalization provided access to topologically and functionally diverse molecular assemblies and laid the groundwork for future studies on ionic-radical transformations and metal-catalyzed intramolecular cyclization reactions.

Site-selective ionic reactions of cobalt-complexed acetylenic tetrads and hexads

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.