A palladium(II)‐catalyzed enantioselective α‐alkylation of azlactones with nonconjugated alkenes is described. The reaction employs a chiral BINOL‐derived phosphoric acid as the source of stereoinduction, and a cleavable bidentate directing group appended to the alkene to control the regioselectivity and stabilize the nucleopalladated alkylpalladium(II) intermediate in the catalytic cycle. A wide range of azlactones were found to be compatible under the optimal reaction conditions to afford products bearing α,α‐disubstituted α‐amino‐acid derivatives with high yields and high enantioselectivity.
The regioselective benzylic C–H alumination of
various symmetrical
and nonsymmetrical 2,6-alkylpyridines catalyzed by a half-sandwich
yttrium complex has been developed. The resulting alkylaluminum species
bearing a pyridyl ring moiety can be transformed to the corresponding
alcohols by oxidation. Moreover, the Cu-catalyzed allylation and benzylation
and Pd-catalyzed arylation reactions can be applied to the resulting
alkylaluminum species, giving the corresponding α-mono-allylated,
α-mono-benzylated, and α-mono-arylated 2-alkylpyridine
derivatives, respectively, in good to high yields. Unsymmetrically
substituted 2,6-dialkylpyridines can be synthesized from simple symmetrical
substrates by repeating such C–H alumination/C–C bond
formation processes. Because of the high regioselectivity of the present
C–H alumination and the subsequent C–C bond formation,
this protocol may serve as a desirable method for the synthesis of
nonsymmetrically-2,6-disubstituted pyridine derivatives.
Surface-tethered polymers have important applications
in functional
polymer coatings, particularly for the development of chemically responsive
surfaces. Here, we combined the traditional grafting-to and grafting-from
methods to create a new surface grafting strategy, termed grafting-to
and from, using surface-initiated ring-opening metathesis polymerization
(SI-ROMP). In this method, poly(pentafluorophenyl methacrylate) is
grafted to an amine terminated surface. Surplus reactive esters after
reaction with surface amines render this polymer a connecting or tie
layer that can be further reacted to provide dense ROMP initiation
sites. This amplification of grafting sites results in thick and environmentally
stable polymer brushes upon SI-ROMP. With the goal of developing polymer-grafted
breathable membranes that autonomously react to multiple chemical
warfare agents (CWAs), we demonstrate the benefit of this method by
employing amine reactive monomers in the grafting-from step. This
enables diverse postsynthetic functionalization for the facile screening
of chemical motifs to enhance response capabilities to mustard blister
agents. Surface-tethered triarylmethanol-containing polymers with
four distinct functional groups are prepared and challenged with the
vapor of 2-chloroethyl ethyl sulfide (CEES), a simulant of mustard
agent, in humid air. Importantly, hydroxyl groups effectively improve
CWA response and the resulting polymer brushes show chain collapse
after both CEES and diethylchlorophosphate (DCP) treatment. Our results
illustrate that the grafting-to and from method can be used to grow
functional and robust polymer coatings for various applications.
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