Asymmetric Allylic Etherification of Vinylethylene Carbonates with Diols via Pd/B Cooperative Catalysis: A Route to Chiral Hemi-Crown Ethers

Abstract

Pd-catalyzed regio- and enantioselective allylic etherification of vinylethylene carbonates (VECs) with diols has been developed. By using cooperative catalysts of the chiral palladium complex and triethylborane in mild conditions, the process gave monoetherified and bisetherified polyglycol derivatives with tetrasubstituted stereocenters in high yields with complete regioselectivities and high levels of enantio- and diastereoselectivities.

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

“…More recently, the same authors expanded their work to diols, which could be converted into mono- and bisetherified polyglycol derivatives with complete regioselectivity and excellent enantio- and diastereoselectivities (up to >99% ee and up to >20/1 dr). 85 …”

Asymmetric Aminomethylative Etherification of Conjugated Dienes with Aliphatic Alcohols Facilitated by Hydrogen Bonding

“…Early studies on the alcohol activation largely relied on the use of extra metals to soften the oxygen nucleophiles, which not only suffered from the requirement of a stoichiometric amount of metals but also resulted in intricately poor regioselectivity . As a means of addressing these problems, an elegant approach by the formation of borate complex was developed by Trost and others, which allowed for the efficient allylic etherification of isoprene oxides and vinylethylene carbonates . Unfortunately, such a method was restricted only to the substrates that could form zwitterionic π-allylpalladium intermediates.…”

“…To overcome these limitations, we envisioned a new strategy to activate alcohols by formation of hydrogen bonds between the alcohol and a hydrogen bond acceptor embellished π-allylpalladium species, in which the hydrogen bond acceptor is catalytically installed during the formation of the π-allylpalladium species (Scheme A). Similar to the activation of alcohols by the formation of a borate complex with zwitterionic π-allylpalladium species, the hydrogen-bonding interaction between the functionalized π-allylpalladium species and alcohols not only can enhance the ability of the alcohols to serve as good nucleophiles but also can improve the regioselectivity by temporarily tethering the alcohols close to the reaction site. It is conceivable that the successful implementation of this strategy calls for the identification of a suitable hydrogen bond acceptor and an efficient process to install it to some readily available substrates.…”

Pd-Catalyzed Decarboxylative Cycloaddition of Vinylethylene Carbonates with Isothiocyanates

“…The in situ Pd-catalyzed decarboxylation of the cyclic carbonate provides reactive zwitterionic π-allyl palladium intermediates that can initiate various selective transformations to form diverse allylic and heterocyclic scaffolds. VECs have been used as allylic surrogates to proceed with allylic substitution involving a variety of nucleophiles including water, alcohols, , phenols/thiophenols, amines, sulfinates, , carbon nucleophiles, etc. Regio- and stereoselective formations of substituted allylic compounds have been efficiently obtained using such techniques.…”