نتایج جستجو برای: n disubstituted urea
تعداد نتایج: 1007367 فیلتر نتایج به سال:
Bleach oxidizes trimethylsilyl cyanide to generate an electrophilic cyanating reagent that readily reacts with an amine nucleophile. This oxidative N-cyanation reaction allows for the preparation of disubstituted cyanamides from amines without using highly toxic cyanogen halides.
The regioselective Stille cross-coupling reactions of 3-tri-n-butylstannyl-1-trimethylsilyl-1-propyne demonstrate isomerization following the initial transmetalation step resulting in allenyl palladium intermediates for reductive coupling to yield conjugated 1,1-disubstituted allenylsilanes.
The chiral base n-BuLi/(-)-sparteine or n-BuLi/(+)-sparteine surrogate promotes kinetic resolution of N-Boc-2-arylpiperidines by asymmetric deprotonation. The enantioenriched starting material was recovered with yields 39-48% and ers up to 97 : 3. On lithiation then electrophilic quench, 2,2-disubstituted piperidines were obtained with excellent yields and enantioselectivities.
A systematically varied series of conformationally restricted ketones, readily prepared from N-acetyl-D-glucosamine, were tested against representative olefins as asymmetric epoxidation catalysts showing useful selectivities against terminal olefins and, in particular, typically difficult 2,2-disubstituted terminal olefins.
Regio- and stereoselective hydrostannation of allenes by using di-n-butyliodotin hydride (Bu2SnIH) was accomplished to give alpha,beta-disubstituted vinyltins, which induced the synthesis of multi-substituted alkenes in a one-pot procedure.
A facile method for the preparation of highly active and enantioselective yttrium precatalysts for asymmetric hydroamination of gem-disubstituted aminoalkenes, from the combination of YCl(3) or YCl(3)(THF)(3.5) with ligand (R)- and n-BuLi is described.
Nickel (Ni) is the most recently discovered essential element for higher plants. But there is limited information about the effect of this element on yield and nitrogen (N) metabolism of different plants. In this research, the interaction of Ni supplement and N source was studied on nitrate accumulation and growth of lettuce (Lactuca sativa L. cv. Baker) in solution culture. In a greenhouse exp...
Nitrogen (N) fertilizers are widely used in vegetable production, particularly in leafy vegetables such as sweet basil. Nitrogen fertilizers have high solubility and low efficiency rates and in cropping systems are applied in high amounts that result in different health and environmental problems. Despite their high application, however, the plant’s need of N may not be meet. In this stud...
Three levels of urea (0, 0.5 and 0.75% on fresh weight basis) were added to whole corn plants to investigate their effects on the chemical composition, and digestibility in 16 Ghezel male lambs using a completely randomized design. Rumen degradability and nutritive values were also evaluated. pH, total nitrogen and ammonia-N concentration of silages increased (P<0.05) with the addition of urea....
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