Retention configuration

Optically pure P-ethanolamines react with dichlorocarbene under phase-transfer catalytic conditions to produce epoxides of high configurational retention [30]. Initial reaction occurs at the tertiary nitrogen centre (Scheme 7.29) with subsequent cleavage of the C-N bond. The reaction is configurationally controlled, as shown by the reaction of the conformationally rigid cyclic systems epoxide formation occurs with the equatorial hydroxyl system (50%), but not with the axial hydroxyl compound. 

The next group of [Ru(bpy)2L2] complexes to be considered involves pyridine-based ligands. The structural and spectroscopic properties of cM-[Ru(bpy)2(py)2] have been reported." Hydrolysis of ci5-[Ru(bpy)2(py)Cl] gives cw-[Ru(bpy)2(py)(H20)] with 80% retention of configuration. Retention of configuration also accompanies the oxidation of the latter to cis-[Ru(bpy)2(py)(0)] " ", racemization of which is slow the use of this Ru complex as a chiral oxidant has been examined." The kinetics of the comproportionation reaction between [Ru (bpy)2(py)(0)] " " and [Ru(bpy)2(py)(H20)] + in MeCN have been studied using stopped-fiow methods. The Ru product is unstable, and in MeCN solution undergoes disproportionation... 

C-H bond oxygen insertion, 1163 configuration retention, 1163 epoxidation, 1144-50 hydroperoxy anion transfer, 382 Steric effects hydrogen dioxide, 96-7 peroxide dihedral angle, 101, 177 Steric strain... 

The production of the (Z)-haloalkenes is thought to proceed via initial exchange of the tetrafluoroborate and halide ions and collapse of the resulting vinyliodonium halides by the addition-elimination (Ad-E) mechanism (equations 203 and 204)84. As with Ad-E reactions of moderately activated vinyl halides (X = Cl, Br), which typically occur with configurational retention (> 95%)143 145, the intermediate carbanions apparently prefer a least motion rotation of 60° prior to the expulsion of iodobenzene. It has been demonstrated by an NMR study that anion exchange between (Z)-(2)-phenylsulfonyl-l-decenyl)-phenyliodonium tetrafluoroborate and tetrabutylammonium chloride occurs instantaneously in deuteriochloroform84. Furthermore, when authentic halide salts of the... 

Further exploration125 of the stereochemistry associated with modification of the steroidal side-chain into that of steroidal alkaloids such as solanidine (139) and tomatidine (140) has revealed that on formation of the furan ring in (140) tritium in the 16/8-configuration of cholesterol [as (143)] is retained but appears now in the 16a-configuration. Retention of the tritium excludes a C-16-oxo-intermediate, and the fact that an inversion of configuration is observed excludes hydroxylation with normal retention of configuration. Examination of the fate of the cholesterol 16/S-proton on incorporation into solanidine (139) revealed that during solanidine biosynthesis this proton is lost. 

Numbers in parentheses are the percentage of configuration retention. 6 cis, Reaction with cis-CHF=CHF. 

Since no trans-cis isomerization of the starting materials was observed, the only reasonable reaction path which leads to both trans and cis isomers of the product of each reaction is an initial attack of (SiF2) on the carbon-carbon double bond, followed by rearrangement. The higher ratio of configuration retention for the reaction of cis-difluoroethylene agrees with the known fact that c s-CHF=CHF is more stable than its trans isomer (12). 

Path (i) is ruled out because in both gas-phase and co-condensation experiments no further insertion of SiF2 was observed when pure CH2= CHSiF3 and SiF2 were mixed. Path (ii) was not favored because the ratio of configurational retention of the products CHF—CH(SiF2) F in the reactions of trans- and cis-CHF=CHF increases with n, the number of SiF2 units involved in the products for example, in the reaction of reactions occurred according to (ii), one would expect the order of the retention ratio to be reversed. 

R2CH—OH with configurational retention (equation 3). This Ending may have applications in the synthesis of various hydroxylated natural products based on organodn intermediates. 

Methyl chloroformate in which there are no -hydrogen atoms decomposes only via the substitution reaction . Ethyl chloroformate also decomposes mainly via the substitution reaction , although ethylene formation has been reported at elevated temperatures . Lewis et al have shown that the gas phase decomposition of optically active 2-butyl chloroformate yields 2-chlorobutane with retention of configuration. Retention of configuration has also been demonstrated for the pure liquid , but in ionising solvents inversion can occur , indicating that in such solutions the reaction is partly bimolecular. 

Optically active 0-benzoylatrolactic acid and its methyl ester were reduced to 2-phenylpropionic acids with almost complete loss of optical activity [392]. On the other hand, Nonaka and coworkers [393] found that l-(2-pyridyl)alkanols were reduced to 2-alkylpyridines with configurational retention in acidic medium l-(4-pyridyl)alkanols gave racemic 4-alkylpyridines. The stereochemical course was discussed considering perpendicular adsorption of pyridylalkanol molecules on the cathode and the configurational stability of carbanion intermediates. 

In the case of vinyl carbanions, which may maintain their configuration, retention is observed. Write down the reaction pathway for the electrophilic substitution of c/.s-2-bromo-but-2-ene when it is treated with lithium and then with carbon dioxide. 

The bis(trimethylstannyl) derivative of triquinacene, which can be regarded as a bis(tri-allylstannane), was used for preparing the triquinacene dianion (equation 22-5).22 A secondary benzyl system provides an exception to the rule that the transmetallations involve configurational retention.23... 

S 2 with inversion of configuration S 2 with inversion of configuration retention of configuration... 

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