Can photocatalysis be performed without electron or energy transfer? To address this, organo-photocatalysts that are based on atropisomeric thioureas and display lower excited-state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4-alkenyl-substituted coumarins, which led to the corresponding products with high enantioselectivity (77-96% ee) at low catalyst loading (1-10 mol%). The photocatalytic cycle proceeds by energy sharing via the formation of both static and dynamic complexes (exciplex formation), which is aided by hydrogen bonding.

Nonisocyanate polyurethane (NIPU) thermoset networks were produced from a novel soybean-oil-derived poly­(vinyl ether) (i.e., poly­[(2-vinyoxy)­ethyl soyate]) possessing cyclic carbonate functional groups in the fatty acid ester side chains of the polymer. Three different linear aliphatic diamines, namely, 1,6-hexamethylenediamine, 1,9-nonanediamine, and 1,13-tridecanediamine, were used to cross-link the cyclic carbonate-functional poly­[(2-vinyoxy)­ethyl soyate] [C-poly­(2-VOES)]. All three of these diamines can be readily obtained from renewable resources. For comparison purposes, analogous NIPU networks were produced using cyclic carbonate-functional soybean oil (CSBO) in place of the C-poly­(2-VOES). The chemical, thermal, viscoelastic, and mechanical properties of the six NIPU networks were characterized. With regard to the chemical nature of the soy-based, carbonate-functional component, it was found that the polymeric nature of C-poly­(2-VOES) resulted in very different NIPU properties compared to analogous cross-linked networks based on CSBO. While the CSBO-based NIPU networks exhibited lower Young’s moduli and ductile behavior, the networks based on C-poly­(2-VOES) showed significantly higher Young’s moduli and brittle behavior. In addition, measurements using dynamic mechanical analysis showed significantly high cross-link densities for the networks based on C-poly­(2-VOES), which can be attributed to a much higher number of methine carbon atoms per molecule in C-poly­(2-VOES) as compared to CSBO. In addition to the cross-links resulting from the reaction of the amine groups of the cross-linker with the cyclic carbonate groups of the soy-based carbonate-functional materials, these methine carbon atoms serve as cross-links in the NIPU networks. The higher cross-link densities achieved with the use of C-poly­(2-VOES) explain the thermal and mechanical property differences observed between networks based on the two different soy-based carbonate-functional materials. With regard to the influence of the diamines on NIPU network properties, as expected, increasing the chain length of the diamine cross-linker decreased cross-link density, which, in general, resulted in decreases in Young’s moduli and glass transition temperature.

Direct acyl radical formation of linear aldehydes (RCH2-CHO) and subsequent hydroacylation with electron-deficient olefins can be effected with various types of metal and nonmetal catalysts/reagents. In marked contrast, however, no successful reports on the use of branched aldehydes have been made thus far because of their strong tendency of generating alkyl radicals through the facile decarbonylation of acyl radicals. Here, use of a hypervalent iodine(III) catalyst under visible light photolysis allows a mild way of generating acyl radicals from various branched aldehydes, thereby giving the corresponding hydroacylated products almost exclusively. Another characteristic feature of this approach is the catalytic use of hypervalent iodine(III) reagent, which is a rare example on the generation of radicals in hypervalent iodine chemistry.

A new 100% bio-based thermosetting coating system was developed from epoxidized sucrose soyate crosslinked with blocked bio-based dicarboxylic acids. A solvent-free, green method was used to block the carboxylic acid groups and render the acids miscible with the epoxy resin. The thermal reversibility of this blocking allowed for the formulation of epoxy-acid thermoset coatings that are 100% bio-based. This was possible due to the volatility of the vinyl ethers under curing conditions. These systems have good adhesion to metal substrates and perform well under chemical and physical stress. Additionally, the hardness of the coating system is dependent on the chain length of the diacid used, making it tunable.

Biomass-derived 2,5-furandicarboxylic acid was valorized by conversion to 1,4-naphthalenedicarboxylic acid via benzyne-cycloaddition and reductive aromatization in 66% overall yield (four steps).

A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.

The efficiency of [2+2] photocycloadditions of 4-alkenylcoumarins was evaluated with various thiourea skeletons to develop thiourea-based catalysts for promoting photochemical reactions. Our results indicate that the excited state chemistry is dependent on the nature of the thiourea catalyst employed to activate the photoactive substrate.Keywords: asymmetric photoreactions; hydrogen bonding photocatalysis; organophotocatalysis; photochirogenesis; thiourea photocatalysis Photochemical transformations are an important class of organic reactions that are often known to generate products with unique stereochemistry.[1] For this reason, chemists have developed strategies that are readily applied in organic synthesis.[2] In recent years, there has been tremendous impetus towards developing enantioselective syntheses of complex strained compounds by light initiated reactions. [1c,2i] In that regard three different catalytic strategies have garnered attention, as they are effective in controlling chemical transformations initiated by light. The first strategy involves photoredox chemistry [3] where a light absorbing sensitizer performs a one electron oxidation or reduction of the reactive substrate leading to a radical anion or a radical cation. As these reactive species are in the ground state, their higher potential enables them to react efficiently to form products. The second strategy involves an energy transfer mechanism [2h,4] where the excited state energy from a light absorbing sensitizer is transferred to the substrate, producing a singlet or a triplet excited state that reacts to form the product. This strategy requires the excited state energy of the sensitizer to be higher than that of the reactive substrate. The third strategy involves an energy sharing mechanism where, upon light excitation, the sensitizer/catalyst and reactant complex (static/dynamic complex) undergo a phototransformation to form the product(s). [5] We have embraced the energy sharing strategy and have utilized thiourea-based catalysts [6] to promote photoreactions with excellent control of product enantioselectivity.[5b] As an example, we showed that 4-alkenylcoumarin 1a underwent a stereoselective [2+2] photocycloaddition to form photoproduct 2a with 94% enantioselectivity with binaphthyl based thiourea catalysts.[5b] Having deciphered the importance of binaphthyl based thiourea catalysts we were interested in evaluating other thiourea skeletons to promote photochemical transformations. We were interested in the role of thioureas not only to achieve high enantioselectivity but also high conversions, as it will increase the type of skeletons that could be employed for controlling photoreactions. In this report we present our findings with six diverse thiourea catalysts 3b-g in promoting the [2+2] photocycloaddition of coumarins 1a and 1b. (Scheme 1). The efficiencies of the new thiourea skeletons were compared to reaction efficiency with our previously established catalyst 3a (prepared in one step from commercially availab...

A cinchona alkaloid-derived urea was found to be an efficient organocatalyst for catalyzing enantioselective conjugate addition between thiols and various alpha,beta-unsaturated ketones to provide optically active sulfides with high chemical yields (up to >99%) and enantiomeric excess (up to >99% ee). The reaction was performed with 0.1 mol % of catalyst in toluene at room temperature. A transition state model has been proposed to explain the stereochemical outcome of the reaction.