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T Pei

Publications and source records attributed to T Pei.

7 recordsLinked to original sources
PubMed2001

Palladium-catalyzed asymmetric diene cyclization/hydrosilylation employing functionalized silanes and disiloxanes.

Pentasubstituted disiloxanes and silanes of the form HSiMe(2)CH(x)Ph(3-x)(x = 1 or 2) reacted with dimethyl diallylmalonate (1) and other functionalized 1,6-dienes in the presence of a catalytic 1:1 mixture of (N-N)Pd(Me)Cl [N-N = (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline] [(R)-2] and NaBAr(4) [Ar = 3,5-C(6)H(3)(CF(3))(2)] to form the corresponding silylated cyclopentanes in good yield with high diastereoselectivity. The enantioselectivity of cyclization/hydrosilylation of 1 with disiloxanes and functionalized silanes at -20 degrees C increased in the following order: HSiMe(2)OSiMe(3) (75% ee) < HSiMe(2)OSiMe(2)-t-Bu (80% ee) < HSi(i-Pr)(2)OSiMe(3) (86% ee) = HSiMe(2)Bn (86% ee) < HSiMe(2)OSi(i-Pr)(3) (89% ee) < HSiMe(2)OSiPh(2)-t-Bu (91% ee) < HSiMe(2)CHPh(2) (93% ee). Silylated cyclopentanes derived from HSiMe(2)OSiMe(3) were oxidized with excess KF and peracetic acid at room temperature for 48 h to form the corresponding hydroxymethylcyclopentanes in good yield (82-95%). Silylated cyclopentanes derived from HSiMe(2)OSiPh(2)t-Bu were oxidized with a mixture of tetrabutylammonium fluoride and either H(2)O(2) or peracetic acid to form the corresponding alcohols in 48-76% yield. Silylated carbocycles generated from benzhydryldimethylsilane were oxidized with a mixture of TBAF/KHCO(3)/H(2)O(2) in 71-98% yield. Asymmetric cyclization/hydrosilylation/oxidation employing benzhydryldimethylsilane tolerated allylic and terminal olefinic substitution and a range of functional groups.

Benzhydryl Compounds↗
PubMed2000

Enantioselective diene Cyclization/Hydrosilylation catalyzed by optically active palladium bisoxazoline and pyridine-oxazoline complexes.

A 1:1 mixture of (N-N)Pd(Me)Cl ¿N-N = (S,S)-4,4'-dibenzyl-4,5,4', 5'-tetrahydro-2,2'-bisoxazoline (S,S-4a) and NaBAr(4) ¿Ar = 3, 5-C(6)H(3)(CF(3))(2) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of dimethyl diallylmalonate (2) and triethylsilane at -30 degrees C for 48 h to form an 8.1:1 mixture of the silylated carbocycle (S,S)-trans-1, 1-dicarbomethoxy-4-methyl-3-¿(triethylsilyl)methylcyclop ent ane (S, S-3) (95% de, 72% ee) and dimethyl 3,4-dimethylcyclopentane-1, 1-dicarboxylate (S,S-6) in 64% combined yield. In comparison, a 1:1 mixture of the palladium pyridine-oxazoline complex (N-N)Pd(Me)Cl ¿N-N = (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline (R-5b) and NaBAr(4) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of 2 and triethylsilane at -32 degrees C for 24 h to form carbocycle S,S-3 in 82% yield (>95% de, 87% ee) as the exclusive product. Asymmetric diene cyclization catalyzed by complex R-5b was compatible with a range of functional groups and produced carbocycles with up to 91% ee. The procedure also tolerated substitution at a terminal olefinic position and at the allylic position of the diene.

Boron Compounds↗
PubMed2000

Use of pentamethyldisiloxane in the palladium-catalyzed cyclization/hydrosilylation of functionalized dienes.

[reaction--see text] Pentamethyldisiloxane reacts with a range of functionalized dienes in the presence of a catalytic 1:1 mixture of (N-N)Pd(Me)Cl [N-N = 1, 10-phenanthroline or (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline] and NaBAr(4) [Ar = 3,5-C(6)H(3)(CF(3))(2)] to form the corresponding silylated carbocycles in good yield and with good stereoselectivity. Treatment of these silylated carbocycles with excess KF and peracetic acid at room temperature for 48 h formed the corresponding alcohols in excellent yield with retention of stereochemistry.

Catalysis↗
PubMed2000

[Rainfall interception capacity of forest canopy between two different stands].

Based on the observation data, the rainfall interception capacity of the canopy in plantation and natural forest stands and its relation to rainfall were examined using the method of taking maximum under the same rainfall. The results showed that the rainfall interception capacity of plantation forest increased rapidly with the increase of rainfall, because of its even distribution of branches and leaves, which was higher under low rainfall less than 30 mm, and the saturation interception capacity was easily reached, depending on the quantity of branches and leaves in the canopy. Although the interception capacity of natural forest was relatively weak under low rainfall less than 30 mm, compared with plantation forest, it was much stronger under heavy rainfall more than 30 mm. The saturation interception of natural forest was larger than that of plantation forest.

Ecosystem↗
PubMed2000

[Effect of unsymmetrical cutting along both river slopes on rainstorm-runoff process].

A simulation experiment was conducted to compare the effect of cutting and no-cutting at both slopes along a river on the rainstorm run-off in catchment, and a model was constructed. The results showed that the appearance of outflow and peak flow of surface run-off was later on forest slope than on forest-cutting slope. On forest slope, the duration was prolonged, and the peak flow and surface runoff were lower. These effects were more obvious as the slope gradient was bigger. When rain intensity was 1.98 mm.min-1 and rainfall was 108.8 mm, the peak flow and the total runoff on both forested slopes of gradient 15 degrees was 5% and 4% less than that on the cutting slopes, respectively.

Rain↗