Remote Fluorination of α,ß-Unsaturated Carbonyls via Silyl Dienol Ethers.

We report a general, regioselective, and metal free γ-fluorination of α,ß-unsaturated carbonyls via silyl dienol ethers that are readily prepared from simple ketones and aldehydes. The transformation displays broad scope including 27 cyclic and acyclic siloxydienes providing γ-fluoro compounds in 28-91 % yield. Notably, the reported conditions are also suitable for the synthesis of challenging tertiary fluorides. The regioselectivity of the reaction was studied on a series of acyclic siloxydienes and was observed to be sensitive to the conformational flexibility of the substrate. Diversification of the γ-fluorocarbonyls demonstrates the promise of fluorine as a stereocontrol element.

Iron-Catalyzed Gamma-Gamma Dimerization of Siloxydienes.

We report the oxidative dimerization reaction of siloxydienes derived from simple enones that creates a new gamma-gamma (γ-γ) C-C bond using catalytic iron and benzoyl peroxide as the terminal oxidant in acetonitrile solvent at ambient temperature. The reaction shows a broad substrate scope including cyclic and acyclic siloxydienes derived from ketones, aldehydes, and esters, which are converted to 1,8-dicarbonyl compounds under mild catalytic reaction conditions in 19-89 % yield across 30 examples. The method is suitable for the coupling of sterically demanding carbon centers, including the formation of vicinal quaternary centers. Conceptually, the dienol ether serves as a precursor to a conjugated radical cation, which undergoes highly site selective γ-dimerization reactions. The γ-γ dimerization strategy is applied to the synthesis of a bioactive analogue of honokiol.

Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions.

Redox-active proanions of the type B12(OCH2Ar)12 [Ar = C6F5 (1), 4-CF3C6H4 (2), 3,5-(CF3)2C6H3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1-3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (Mn) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH2Cl2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1-3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA.

Dynamics of amphiphilic block copolymers in an aqueous solution: direct imaging of micelle formation and nanoparticle encapsulation.

Micelles formed through the aggregation of amphiphilic block copolymers are ideal drug nanocarriers. Despite their importance in nanomedicine, the detailed mechanisms through which micelles form and copolymers encapsulate the target nanomaterials are unclear. Here, using in situ liquid cell transmission electron microscopy imaging, we capture both the dynamics of micelle formation and their encapsulation of gold nanoparticles (NPs) in an aqueous solution. Our observations reveal that the amphiphilic block copolymers aggregate and rearrange to form a micelle with a hydrophobic and rigid core, surrounded by a corona of hydrophilic blocks that extend into the solution. These micelles are stable against coalescence, and once mature, they do not merge. We also show that the encapsulation of hydrophobic NPs is a self-limiting process, which occurs through gradual adsorption of block copolymers; the growth of a polymeric shell around the NPs, shielding them from water, ceases when the NPs are fully covered by the adsorbed copolymers. The insights from these observations are of fundamental importance for the design of biocompatible soft materials.

Omniphilic Polysaccharide-Based Nanocarriers for Modular Molecular Delivery in a Broad Range of Biosystems.

Self-adjusting omniphilic nanocarriers (OPNs) with a multisolvent aptitude were prepared via a Schiff base reaction between chitosan, a natural polysaccharide, and bioactive aldehydes. Experimental studies supported by atomistic molecular dynamics simulations revealed these OPNs can encapsulate insoluble molecular cargo, transport them in aqueous or lipid environments, and deliver them through cross-phase barriers. N-imine dynamic covalent bonds have been incorporated to endow the OPNs with pH responsiveness, also allowing the amplification of their bioactivity, as demonstrated in vitro with the ability to delay fungal proliferation in wheat grains. The reported OPNs hold remarkable potential as biocompatible nanocarriers for the effective delivery of active agents in agriculture, medicine, and cosmetics.

Publisher Correction: Reversible chromism of spiropyran in the cavity of a flexible coordination cage.

The original version of this Article contained an error in Fig. 4c, in which the right-most chemical structure included an 'N+' rather than an 'N'. This has been corrected in both the PDF and HTML versions of the Article.

Reversible chromism of spiropyran in the cavity of a flexible coordination cage.

Confining molecules to volumes only slightly larger than the molecules themselves can profoundly alter their properties. Molecular switches-entities that can be toggled between two or more forms upon exposure to an external stimulus-often require conformational freedom to isomerize. Therefore, placing these switches in confined spaces can render them non-operational. To preserve the switchability of these species under confinement, we work with a water-soluble coordination cage that is flexible enough to adapt its shape to the conformation of the encapsulated guest. We show that owing to its flexibility, the cage is not only capable of accommodating-and solubilizing in water-several light-responsive spiropyran-based molecular switches, but, more importantly, it also provides an environment suitable for the efficient, reversible photoisomerization of the bound guests. Our findings pave the way towards studying various molecular switching processes in confined environments.