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Julia olefination has advantages over other olefination techniques in that it offers mild user-friendly conditions over a wide range of substrates. Perhaps the most well-known Julia-Kocienski olefination method, colloquially known as the Modified Julia, uses heteroaromatic sulfone moieties like 1-methyl methylsulfonyl benzimidazole to furnish the transformation. The inclusion of heteroatoms into the aromatic handle modifies the mechanistic pathway resulting in a one-pot procedure and the evolution of SO 2 gas driving the reaction to completion.
Ando, T. Kobayashi, N. Uchida, Org. Julia, J. Paris, Tetrahedron Lett. Review literature The modified Julia olefination: alkene synthesis via the condensation of metallated heteroarylalkylsulfones with carbonyl compounds P.
Blakemore, J. Page Top.
The addition of a phenylsulfonyl carbanion to an aldehyde or ketone leads to an intermediate alcohol, which is esterified in situ. The reductive elimination with sodium amalgam to furnish the alkene takes place in a second step. The Julia-Kociensky Olefination is an alternative procedure, which leads to the olefin in one step. A first possible mechanism proceeds through a planar radical that can rotate freely about the C-C bond. Both diastereomers would thus pass through the same radical intermediate, which can be used to explain the E -selectivity.
Julia Olefination Reaction
Animation controls: Display controls:. Click the structures and reaction black arrows in sequence to view the 3D models and animations respectively. NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition state phase. Initial base promoted elimination of carboxylate leads to a vinyl sulphone which is reductively cleaved to a vinyl radical. The stereoselectivity of the Julia olefination is determined by the radical intermediate.
The Modified Julia Olefination enables the preparation of alkenes from benzothiazolyl sulfones and aldehydes in a single step:. Whether the anti or syn intermediate is generated can be influenced to some extent by the choice of reaction conditions:. The intermediates that form react further to give E - and Z -isomers of the alkene:. A mechanistically related nucleophilic addition of the sulfonyl carbanion to a second equivalent of the BT sulfone leads to a side product. The benzothiazolyl group BT can play several roles: in one, it enables a more or less strongly pronounced complexation that influences the selectivity; on the other hand, it can also undergo nucleophilic substitution at the carbon attached to the sulfonyl group, which then becomes a leaving group. Other hetero cyclic substituents can assume these roles, and offer somewhat different selectivity:.