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In the example shown below, the para-methoxybenzoyl substituent serves primarily as a source of steric bulk to allow the catalyst to differentiate the two faces of the alkene. [23] SAD scheme 3. It is often difficult to obtain high diastereoselectivity on cis-disubstituted alkenes when both ends of the olefin have similar steric environments.
The Grieco elimination is an organic reaction describing the elimination reaction of an aliphatic primary alcohol through a selenide to a terminal alkene. [1] [2] It is named for Paul Grieco. The alcohol first reacts with o-nitrophenylselenocyanate and tributylphosphine to form a selenide via a nucleophilic substitution on the electron ...
Reduction of alkynes is a useful method for the stereoselective synthesis of disubstituted alkenes. If the cis -alkene is desired, hydrogenation in the presence of Lindlar's catalyst (a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead) is commonly used, though hydroboration ...
A notable variant of the Huisgen 1,3-dipolar cycloaddition is the copper(I) catalyzed variant, no longer a true concerted cycloaddition, in which organic azides and terminal alkynes are united to afford 1,4-regioisomers of 1,2,3-triazoles as sole products (substitution at positions 1' and 4' as shown above).
Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the steric properties of the substituents are very different. For such 1,2-disubstituted olefins, regioselectivity can be observed only when one of the two substituents is a phenyl ring.
The configuration of the olefin is retained in the cycloaddition product. Electron-withdrawing substituents on the ketene and donating substituents on the alkene accelerate the reaction, [6] but disubstituted ketenes react slowly due to steric hindrance. [7] Orbital coefficients can be used to determine regioselectivity.
The Kulinkovich reaction describes the organic synthesis of substituted cyclopropanols through reaction of esters with dialkyldialkoxytitanium reagents, which are generated in situ from Grignard reagents containing a hydrogen in beta-position and titanium(IV) alkoxides such as titanium isopropoxide. [1]
Allylic oxidation can be predicted by the substitution pattern on the olefin. In the case of 1,2-disubstituted olefins, reaction rates follow CH > CH 2 > CH 3: Geminally-substituted olefins react in the same order of reaction rates as above: [2] Trisubstituted alkenes experience reactivity at the more substituted end of the double bond.