Light- and humidity-responsive chiral nematic photonic crystal (PC) films containing cellulose nanocrystals (CNCs) were fabricated. A photoactive polymer with hydrophilic groups, poly-(3,3′-benzophenone-4,4′-dicarboxylic acid dicarboxylate polyethylene glycol) ester, was coassembled with CNCs to form flexible iridescent films with a tunable chiral nematic order. In the coassembly process, the intermolecular hydrogen bonds of CNCs were weakened, which facilitated the fine regulation of the chiral PC nanostructure. The PC films displayed sensitive responses to both light and humidity. With increasing humidity from 30 to 100%, the chiral nematic helix pitch increased from 328 to 422 nm. The color of the PC films changed from blue to green, yellow, orange, and dark red with increasing relative humidity. Over 15 min of light irradiation, the absorption intensity of the films increased gradually. The light and humidity responses of the films were reversible. The films maintained their variable cholesteric liquid crystal texture and helical lamellar structure after light irradiation at different humidities. These PC films are expected to be useful in intelligent coatings and 3D printing.

Pd-catalyzed aerobic oxidative coupling of vinylboronic acids and electronically unbiased alkyl olefins provides regioselective access to 1,3-disubstituted conjugated dienes. Catalyst-controlled regioselectivity is achieved by using 2,9-dimethylphenanthroline as a ligand. The observed regioselectivity is opposite to that observed from a traditional (non-oxidative) Heck reaction between a vinyl bromide and an alkene. DFT computational studies reveal that steric effects of the 2,9-dimethylphenanthroline ligand promote C–C bond-formation at the internal position of the alkene.

A new dicationic PdII catalyst, employing a 6,6'-dimethylbipyridine ligand, has been identified that is capable of promoting both aerobic oxidative Heck coupling and dehydrogenation reactions of cyclohexenones. These reactions may be combined in a one-pot sequence to enable the straightforward synthesis of meta-substituted phenols.

Abstract:The asymmetric construction of quaternary carbon centers via cross-aldol reactions of ketones with b,g-unsaturated keto esters catalyzed by 4-(tert-butyldiphenylsilyloxy)-pyrrolidine-2-carboxylic acid in water is described. The adducts bearing two adjacent chiral centers were obtained in high yields, mostly up to 99% ee, and with high diastereoselectivities. The corresponding polyfunctional products could also be easily transformed to useful lactones with three chiral centers.

Chiral liquid crystal materials that are responsive to environmental stimuli are in demand. A chiral photonic crystal membrane based on cellulose nanocrystals (CNCs) was prepared by molecule assembly in the present work. A fluorescent molecule containing a cationic group, [N-(3-N-benzyl-N,N-dimethylpropyl ammonium chloride)-1,8-naphthalimide]­hydrazine, was assembled on the surface of the CNCs. The new chiral photonic crystal membrane possesses supersensitive multiresponses to small molecules, such as water and formaldehyde molecules. The appearance, liquid crystal texture, fluorescence, and color of the chiral membrane have sensitive changes induced by small molecules. By increasing RH from 30 to 100%, the reflectance peak of the membrane red-shifted from 498 to 736 nm. In particular, the iridescent texture and fingerprint structure of the membrane could change markedly under trace amounts of formaldehyde, and the chiral membrane can form an extremely sensitive off–on fluorescence switch. The relationship between the fluorescence intensity and the trace concentration of formaldehyde satisfied the linear equation with the association coefficient of 0.9997. The changes in fluorescence and color are visible to the naked eye, and the membrane can quantitatively recognize trace formaldehyde at a molecular level in a humid environment. The mechanism by which the fluorescence switch operates was investigated using density functional theory at the B3LYP/6-31G­(d) level. The membrane has potential for use in the fields of advanced functional materials and biomaterials.

A highly enantioselective Michael addition of cyclic 1,3-dicarbonyl compounds to b,g-unsaturated a-keto esters catalyzed by amino acid-derived thiourea-tertiary-amine catalysts is presented. Using 5 mol% of a novel tyrosine-derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time.Keywords: 1,3-dicarbonyl compounds; Michael addition; organocatalysts; thioureas; b,g-unsaturated a-keto esters Increased focus has recently been placed on the application of organocatalysis in reactions allowing the rapid construction of functionalized molecules from simple and readily available starting materials.[1] In this field, the asymmetric Michael addition of 1,3-cyclic dicarbonyl compounds to a,b-unsaturated carbonyl systems, which could provide many chiral compounds with biological and pharmaceutical activities such as neo-flavonoids and coumarins, has attracted much attention.[2] As a class of activated a,b-unsaturated carbonyl systems, b,g-unsaturated a-keto esters sometimes are preferred electrophiles in this kind of reaction due to their high reactivity and the easy convertibility of the resultant products to other useful structures.[3] In 2003, Jørgensen et al. reported the enantioselective Michael addition of cyclic 1,3-dicarbonyl compounds to b,g-unsaturated a-keto esters catalyzed by chiral bisoxazoline-copper(II) complexes with moderate to high enantioselectivities.[4] However, it was not until very recently that an similar organocatalyzed reaction between cyclic diketones and b,g-unsaturated a-keto esters using Cinchona alkaloid-derived pyrimidines was reported by Calter et al. [5] In contrast, several organocatalysts have been developed for the Michael addition of cyclic diketones to a,b-unsaturated ketones, in which the "imine catalysis" usually controls the enantioselectivity. [6] On the other hand, following the pioneering works of Jacobsen and Takemoto, [7] remarkable advances have been made in the development and application of bifunctional chiral thiourea catalysts in catalytic asymmetric reactions. [8] Recently, the use of inexpensive and readily available amino acids as the chiral scaffold to develop novel thiourea catalysts has attracted considerable interest and proved to be effective in several asymmetric reactions.[9] Our group has been interested in the development of organocatalytic reactions utilizing b,g-unsaturated a-keto esters as a reaction partner to synthesize useful compounds. [10] We report herein the development of several amino acid-derived thiourea-tertiary amine catalysts and their applications to the asymmetric Michael addition of cyclic 1,3-dicarbonyl compounds to b,g-unsaturated a-keto esters.Using the reaction between (E)-methyl 2-oxo-4-phenylbut-3-enoate (3a) and 4-hydroxycoumarin (4a) as the model reaction, a series of thiourea-tertiary amine catalysts (Figure 1) was evaluated and the results are summarized in Table 1. Similar to Takemotos ca...

Bifunctional catalyst: Simple bifunctional N‐Acyl aminophosphines such as 1 were developed to catalyze the first asymmetric [3+2] cycloaddition between allenoates and dual activated olefins. The cycloaddition reactions afford multifunctional chiral cyclopentenes with exclusive regioselectivity, and good to excellent enantioselectivity and yields.

Branched-selective oxidative Heck coupling reactions have been developed between arylboronic acids and electronically unbiased terminal alkenes. The reactions exhibit high catalyst-controlled regioselectivity favoring the less common branched isomer. The reactions employ a catalyst composed of Pd(TFA)2/dmphen (TFA = trifluoroacetate, dmphen = 2,9-dimethyl-1,10-phenanthroline) and proceed efficiently at 45-60 °C under 1 atm of O2 without requiring other additives. A broad array of functional groups, including aryl halide, allyl silane and carboxylic acids are tolerated.