A variety of secondary benzylic amines were oxidized to imines in 90% to >99% yields by singlet oxygen generated from oxygen and a porphyrin photosensitizer. On the basis of these reactions, a protocol was developed for oxidative Ugi-type reactions with singlet oxygen as the oxidant. This protocol has been used to synthesize C1- and N-functionalized benzylic amines in up to 96% yields.

Tsuji-Trost allylations are Pd 0 -catalyzed reactions in which diverse nucleophiles are allylated with allylic alcohol derivatives such as allylic acetates.[1] Asymmetric catalysis of these reactions is commonly achieved by the use of chiral neutral ligands. [1,2] We have recently described a different approach that is based on the use of chiral counteranions, which are introduced to the reaction in catalytic amounts. [3,4] We discovered an asymmetric a-allylation of a-branched aldehydes using benzhydryl allyl amine as the allylating reagent and a combination of [Pd(PPh 3 ) 4 ] and the chiral Brønsted acid TRIP as catalysts.[4a] Herein, we report the first example of a highly enantioselective a-allylation of aldehydes with simple allylic alcohols [Eq. (1)]. This reaction is catalyzed by the concerted action of three different species, [Pd(PPh 3 ) 4 ], benzhydryl amine, and TRIP, and constitutes another example of asymmetric counteranion-directed catalysis (ACDC). [4] While great progress in the asymmetric catalysis of TsujiTrost-type allylations has been made in recent years, the direct use of allylic alcohols as allylating reagents is extremely rare [5] and even entirely unprecedented with carbonyl nucleophiles. [6,7] Continuing our studies on the use of chiral counteranions in asymmetric Pd catalysis, [4a] we recently became interested in further simplifying and potentially improving our previous protocol by directly utilizing simple allylic alcohols rather than benzhydryl allyl amines, which have to be synthesized individually in a separate step.In our previous allylation studies, we have suggested that our reaction involves the generation of the equivalent of a pallyl-Pd-TRIP ion pair as the critical intermediate, which reacts with an enamine generated from the released benzhydryl amine and the aldehyde. We reasoned that the same pallyl-Pd complex should also be generable from allylic alcohol and the combined action of TRIP and [Pd(PPh 3 ) 4 ]. Indeed, very recently we have shown that a simple achiral Brønsted acid and [Pd(PPh 3 ) 4 ] constitutes a powerful catalyst pair for nonasymmetric a-allylations of aldehydes, [8] suggesting that the concentration and nucleophilicity of the aldehyde-derived enol is sufficient for the reaction to occur. This transformation proceeds via a mass-spectrometrically detectable p-allyl-Pd intermediate and not through a Claisen mechanism, [6a,b] and no reaction occurs in the absence of Pd. However, while we were delighted to find that TRIP and [Pd(PPh 3 ) 4 ] indeed readily catalyze the a-allylation of hydratropic aldehyde (2-phenylpropanal, 1 a) with allylic alcohol (2 a), the enantiomeric ratio of product 3 a was disappointingly minuscule [Eq. (2)].We hypothesized that the low enantioselectivity can be attributed to the fact that both E-and Z-enol isomers are generated under our reaction conditions but lead to opposite enantiomeric products (Figure 1). In our previous and highly enantioselective variant, a benzhydryl amine derived enamine was invoked, of which we expect the ...

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Gas exchange, chlorophyll fluorescence, and contents of some metabolites in two Japanese honeysuckle (Lonicera japonica Thunb.) cultivars, Damaohua (2n = 2x) and Jiufengyihao (2n = 4x), were compared with explore the function of chromosome doubling under water stress conditions. Water stress significantly decreased net photosynthesis rate, stomatal conductance, and transpiration rate of both cultivars. It also decreased electron transport rate, effective quantum yield of Photosystem II, photochemical quenching, and starch content, but increased non-photochemical quenching and contents of total soluble sugars, proline, and malondialdehyde. However, the tetraploid cultivar showed higher resistance to water stress than the diploid, as indicated by the fact that gas exchange, chlorophyll fluorescence, and metabolites were less affected for the tetraploid than the diploid. Moreover, the tetraploid recovered more quickly than the diploid after re-watering. Morphological and anatomical analysis further revealed that the tetraploid possessed less whole plant leaf area, higher leaf mass per unit area, thicker epidermis (both upper and lower) and palisade tissue, as well as denser pubescence. All of those specialised structures caused by chromosome doubling might lead to greater capacity in coping with drought stress. Our findings suggest that the effect of chromosome doubling on drought resistance in L. japonica could attribute to the improvement of structure and photosynthesis-related traits.

The photoprotection of energy dissipation and water-water cycle were investigated by comparing chilling sensitivity of photosystems 2 (PS2) and 1 (PS1) in two chilling-sensitive plants, cucumber and sweet pepper, upon exposure to 4 °C under low irradiance (100 µmol m -2 s -1 ) for 6 h. During chilling stress, the maximum photochemical efficiency of PS2 (F v /F m ) decreased only slightly in both plants, but the oxidisable P700 decreased markedly, which indicated that PS1 was more sensitive to chilling treatment under low irradiance than PS2. Sweet pepper leaves had lower F v /F m , higher nonphotochemical quenching (NPQ), and higher oxidisable P700 during chilling stress. Activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in cucumber leaves was higher, but APX activity decreased apparently compared to that at room temperature. The productions of active oxygen species (H 2 O 2 , O 2 ¯·) increased in both plants, faster in cucumber leaves than in sweet pepper leaves. In sweet pepper leaves, a stronger de-epoxidation of the xanthophyll cycle pigments, a higher NPQ could act as a major protective mechanism to reduce the formation of active oxygen species during stress. Thus sensitivity of both plants to chilling under low irradiance was dominated by the protective mechanisms between PS1 and PS2, especially the energy dissipation and the water-water cycle.

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Nitrogen (N) resorption from senescing tissues enables plants to conserve and reuse this important nutrient. As such, it is expected that plant species adapted to infertile soils could have a higher N-resorption efficiency (percentage reduction of nitrogen between green and senescing tissues) and/or higher N-resorption proficiency (absolute reduction of nitrogen in senescing tissues) than those adapted to fertile soils. To test this hypothesis, we investigated the relationships among soil characteristics (total N, nitrate-N, ammonium-N, pH and moisture) and N resorption in Stipa krylovii Roshev., a species occurred widely in natural grasslands of northern China. N contents in green and senescing tissues were 6.7 ± 0.1 and 3.3 ± 0.1 mg g )1 , respectively. The mean value of N-resorption efficiency was found to be 72.1%. The N-resorption efficiency in S. krylovii was independent of soil characteristics. The N-resorption proficiency in S. krylovii was dependent on soil nitrate-and ammonium-N, but it was relatively independent of soil total N. The N-resorption proficiency was negatively correlated with soil pH and moisture. There was a positive correlation between N concentration in green tissues and resorption efficiency. However, N-resorption efficiency was not correlated significantly with N concentration in senescing tissues. These results indicate that the intraspecific variation in N resorption of Stipa krylovii Roshev. is associated with soil regimes and that higher N resorption on N-poor soils is an adaptive strategy for S. krylovii to maximize N use under conditions of limited N supply.

Catalytic oxidation of 1‐alkenes to aldehydes by an epoxidation–isomerization pathway with air or dioxygen as terminal oxidant has been realized for bulky ruthenium(VI) porphyrin catalysts. For the new, recyclable catalyst [RuVI(tmttp)O2], product yields of up to 99 % and total turnover numbers of up to 1144 were obtained.