Stereochemistry of formation

The stereochemistry of formation and rearrangement of vicinal dihaUdes has been elucidated, chiefly by Barton s group. Trans diaxial addition occurs but the product may then equilibrate with the more stable... 

A comparison of the stereochemistry of the 2-vinyl pyridine addition to [2a] with that of methylation addition is particularly instructive. Table 2 shows the stereochemistry of formation of [7a] as a function of counterion size and coordination. 

Stereochemistry of Formation of 2,4,6-Tri(2-pyridyl)-heptane As a Function of Cation and Cation Coordination in THF at -78°C... 

Figure 12-13 The stereochemistry of formation of a tetrahedral intermediate by a serine protease. The most probable orientation of groups as deduced by model building is shown. The shaded orbitals in A and B are antiperiplanar to the entering oxygen of Ser 195. See Polgar and Halasz.272...

It is known that electrochemical reduction of oximes in protic media occurs in two steps the N—O bond is first reduced to form an imine and the latter is then reduced to afford a primary amine1,29. Tallec has shown that the amine from oxime 33 can be trapped intramolecularly (equation 16)35. Interestingly, the SS diastereomer predominates the chiral pyrrolidine ring derivative serves to control the stereochemistry of formation of the new benzylic chiral center. Electrochemical reductive cross-coupling of O-methyl oximes with carbonyl compounds in isopropanol at a tin cathode affords adducts (equation 17) which can be reduced further to 2-amino alcohols36. In this fashion, menthone could... 

Full details have been published of the C and incorporation studies on the stereochemistry of formation of the C50 carotenoid decaprenoxan-thin [(2i ,6i ,2 i ,6 / )-2,2 -bis-(4-hydroxy-3-methylbut-2-enyl)-e,e-carotene (195)] (Scheme 4). Both the stereochemistry of the initial electrophilic attack at C-2 and that of the hydrogen loss from C-4 are opposite to those in the C40 series. ... 

Cheng, J C Y, Daves, G D Jr, C-glycosides from palladium-mediated reactions of pyranoid glycals. Stereochemistry of formation of intermediate organopalladium adducts and factors affecting their stability and decomposition, J. Org. Chem., 52, 3083-3090, 1987. 

Other Reactions of Unsaturated Steroids.—Asymmetric synthesis of optically active tricarbonyliron complexes of 1,3-dienes was achieved using the tricar-bonyliron complex (25) as a transfer agent for Fe(CO)3. Further investigation of the stereochemistry of formation of a-(4-6i7)-PdCl complexes from A -3-oxo-... 

When bicyclo[2.2.2]octyl brosylate was solvolyzed in acetic acid containing sodium acetate, the products were a mixture of bicyclo[2.2.2]octyl acetate and bicyclo[3.2.1]octyl acetate, each of which was optically active. The stereochemistry of formation of bicyclo[2.2.2]octyl acetate was concluded to be 82 15% retention of configuration, in accord with that expected for a bridged-ion intermediate. ... 

Numerous papers deal with the chemistry of vitamin B]2> cobalamins, cobinamides, and their synthetic models, the cobaloximes [Co(dmgH)2(R)(L)], including the synthesis of new species,225-228 structural studies,229-239 the stereochemistry of formation and isomerisation,240-244 and reactivity.245-248 jhe effects of viscosity,249 pressure, temperature,250,25l and base coordination252... 

There are two (3 positions. The base (ethoxide) is not sterically hindered, so we expect the Zaitsev product (the more substituted alkene) as the major product. The less substituted alkene will be the minor product. Next, we must identify the stereochemistry of formation of each of the products. Let s begin with the minor product (the less substituted alkene), because its double bond does not exhibit stereoisomerism ... 

An effort was made to examine the stereochemistry of 3-elimination to give a stilbene system but this was thwarted since the first step in the reaction in eq. 7 did not occur to an appreciable extent (20). However the stereochemistry of formation of 2-butene from pyrolysis of the isomeric cyclic and meso -2,3-dimethylsuccinyl peroxides has been accom-piished and found to be the same from either source (eq. 8) ( 1). The reaction in equation 2 was stereospecific as shown, and the resulting E-product is that expected from an anti-elimination from the preferred conformation of the starting material. 

The reagent is methoxide, which is both a strong base and a strong nucleophile. The substrate is secondary so we expect both E2 and 8n2 processes, although E2 will be responsible for the major product. Accordingly, the major product is the more substituted alkene. To determine the stereochemistry of formation of the major product, we must draw a Newman projection. 

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