Templating Photodimerization of <i>trans</i>-Cinnamic Acid Esters with a Water-Soluble Pd Nanocage

A water-soluble octahedral Pd nanocage acting as a reaction vessel templates the photodimerization of substituted trans-cinnamic acid methyl esters in water. Irradiation of the host−guest complexes of trans-cinnamic acid methyl esters with the Pd nanocage resulted in selective formation of a syn head−head dimer in addition to the corresponding cis isomer. These results suggest that the guest molecules are preoriented in a selective fashion with the hydrophilic ester group facing water and the hydrophobic aryl group tucked within the cavity of the host. Such an orientation occurs at the hydrophobic−hydrophilic interface between the nanocage exterior and interior. Weak intermolecular C−H−π and π−π interactions between the host and the guest(s) are likely to be responsible for the lack of mobility of the reactant olefins during their short excited-state lifetime

Enhanced Enantio- and Diastereoselectivities via Confinement: Photorearrangement of 2,4-Cyclohexadienones Included in Zeolites

Employing zeolite as the reaction medium, it is possible to change the enantio (from achiral dienones) and diastereo (from chiral dienones) selectivities during the oxa-di-π-methane rearrangement of 2,4-cyclohexadienones

New Water-Soluble Organic Capsules Are Effective in Controlling Excited-State Processes of Guest Molecules

Synthesis, inclusion properties, and ability to control excited-state properties of two water-soluble hosts are presented. These hosts surround the guest molecule(s) by forming a capsular assembly. By constraining the guest and by providing very little free space, the host is able to alter the excited-state behavior of guest molecules. The excited-state chemistry and physics of guest molecules are distinctly different from those in organic solvents

Templating Photodimerization of Coumarins within a Water-Soluble Nano Reaction Vessel

An octahedral Pd nanocage serves as a reaction vessel to control photodimerization of coumarins in water. The coumarin derivatives explored in this study react within the Pd nanocage to selectively yield a syn head−head dimer, whereas in water, they yield either a mixture of dimers or a different isomer. The selective dimerization is interpreted to mean that the monomers are preorganized by the cage through weak intermolecular forces. The selectivity obtained within the nanocage is more general and predictable compared to other hosts used previously to control the geometry of photodimerization reactions

Supramolecular-Surface Photochemistry: Assembly and Photochemistry of Host–Guest Capsules on Silica Surface

Host cavitands and organic guest molecules independently adsorbed on silica particles when mixed and shaken in the presence of a few drops of water underwent intra- and interparticle migration to form capsular complexes that were not formed either in water or organic solvents. Importance of cavitand migration and tumbling on silica surface was established by demonstrating that covalently linked cavitands do not form capsular complexes. The encapsulated guests exhibited selective photochemistry as they do within an organic capsule in solution

Making a Difference on Excited-State Chemistry by Controlling Free Space within a Nanocapsule: Photochemistry of 1-(4-Alkylphenyl)-3-phenylpropan-2-ones

The free space within a reaction cavity plays a determining role during the excited-state reaction of 1-(4-alkylphenyl)-3-phenylpropan-2-ones included within a capsule formed by two molecules of a deep cavity cavitand. By controlling the free space within the reaction cavity through remote alkyl substitution on the reactant ketone it is possible to control the yield of the rearrangement product shown above

Asymmetric Induction during Yang Cyclization of α-Oxoamides: The Power of a Covalently Linked Chiral Auxiliary Is Enhanced in the Crystalline State

γ-Hydrogen abstraction has been revealed to be the primary photoprocess in the crystalline state of α-oxoamides through photochemical and X-ray structural studies. The outstanding ability of a covalent chiral auxiliary in generating asymmetric induction in the photoproduct β-lactam has been established with 10 examples. We have shown that the crystal lattice preorganizes the reactant molecules toward a single diastereomer of the β-lactam and prevents large motions of the 1,4-diradical intermediate that would result in the loss of stereochemical memory. A rare single-crystal-to-single-crystal transformation path of one of the examples investigated establishes the direct correlation between the stereochemistries of the reactant and the product

Reactive-State Spin-Dependent Diastereoselective Photoisomerization of <i>trans,trans</i>-2,3-Diphenylcyclopropane-1- carboxylic Acid Derivatives Included in Zeolites

The asymmetric induction facilitated by a chiral auxiliary during the photoisomerization of trans,trans-2,3-diphenylcyclopropane derivatives depends on the medium (solution vs zeolite) and the reactive state (singlet vs triplet). Within zeolites, direct excitation most likely proceeds via a zwitterionic intermediate, while triplet sensitization most likely proceeds via a diradical intermediate

Controlling Photochemical Geometric Isomerization of a Stilbene and Dimerization of a Styrene Using a Confined Reaction Cavity in Water

Utility of a water-soluble deep cavity cavitand, octa acid, as a reaction medium is illustrated by carrying out photochemical reactions of a stilbene and a styrene included within the octa acid in water. Geometric isomerization of trans-4,4‘-dimethyl stilbene is restricted while dimerization of 4-methyl styrene is facilitated within the octa acid cavity. The excited-state chemistry of both systems is different in this medium from that in organic solvents. The change in chemistry is attributed to the supramolecular effects provided by the host cavity

Asymmetric Induction during Yang Cyclization of α-Oxoamides: The Power of a Covalently Linked Chiral Auxiliary Is Enhanced in the Crystalline State

γ-Hydrogen abstraction has been revealed to be the primary photoprocess in the crystalline state of α-oxoamides through photochemical and X-ray structural studies. The outstanding ability of a covalent chiral auxiliary in generating asymmetric induction in the photoproduct β-lactam has been established with 10 examples. We have shown that the crystal lattice preorganizes the reactant molecules toward a single diastereomer of the β-lactam and prevents large motions of the 1,4-diradical intermediate that would result in the loss of stereochemical memory. A rare single-crystal-to-single-crystal transformation path of one of the examples investigated establishes the direct correlation between the stereochemistries of the reactant and the product