Ethyl group, 753 table

The transfer of an ethyl group, in particular, can be performed with high diastereoselectivity by the use of tetraalkyllead, activated with titanium(IV) chloride14"15 (Table 4). The order of addition of the reagents exhibits a strong influence on the chemical yield and diastercoselectiv-ity of the addition reaction. Typically, titanium(IV) chloride is added at -78CC to the aldehyde, followed by addition of tetraethyllead. Poor yields and diastereoselectivity are observed if titanium(IV) chloride is first added to tetraethyllead followed by addition of the aldehyde ... 

The data are summarized in Table II. They have been normalized to kx x s i for each zeolite catalyst. In general it is seen that the7transfer of an ethyl group (E,E E,X) occurs faster than that of a methyl group (X,E X,X). This is in agreement with the indicated mechanism for transalkylation (Figure 4) which involves a benzylic carbenium ion intermediate. In the case of methyl transfer, this is a primary cation,... 

The dipolar parts of the analyzed hfs tensors have been compared with calculated values obtained from first order expressions of the electron-nuclear dipole interaction (5.3)57. The coefficients of the atomic orbitals used in this computation, which considers all two- and three-center contributions, are obtained from an extended Huckel calculation (ethyl groups replaced by protons). It has been found that almost 100% of the unpaired electron is located on the CuS4 fragment so that the replacement of the ethyl groups by protons is of minor importance for the calculation of the atomic orbital coefficients. The experimental and theoretical hfs data, summarized in Table 8, are found to... 

Rate constants for Reaction (3.14) were measured directly by LFP techniques and are collected in Table 3.4 [23-27]. These values reflect the overall (ormolecu-lar) reactivity of the substrates regardless of the site or mechanism of the reaction. Mechanistic studies have shown that the attack of the t-BuO radical on EtsSiH occurs in about 80 % of the cases at the SiH moiety and in 20 % at the ethyl groups at 27 °C [23], whereas the attack on (Mc3 Si)3 SiH occurs in about 95 % of the cases at the SiH moiety and in 5 % at the trimethylsilyl groups at 27 °C [26]. 

Table 2.5 lists the additive values for representative fragments/and structural factors F. As an example, the infinite dilution distribution ratio of C2H5 C(0)0C2H5, ethyl propionate, between 1-octanol and water is obtained as follows. The carboxylate group contributes -1.49 to log P, each ethyl group contributes 0.89 -H 0.66 - 0.12 = 1.43 (for the methyl and methylene groups and... 

The enantioselective a-alkylation of /i-oxo esters, e.g., 2-methoxycarbonyl-l-oxoindane and 2-methoxycarbonylcyclohexanone, with optically active alkyl or aryl(cthyl)methyIselenonium and -sulfonium camphorsulfonates or perchlorates, which possess a stereogenic center at the selenonium or sulfonium group, led to a mixture of a-methylated and a-ethylated compounds (Table l)7-10. 

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