1,1-Dimetallic Reagents for the Elaboration of Stereoselectively Di- or Trisubstituted Linear Substrates

Abstract

Although gem-dimetallic species have been known for a long time, and reacted once or twice with electrophiles, the allyl zincation of substituted vinyl metals has emerged as a particularly efficient access to such species. This is due to a high face selectivity, in the addition to the C=C bond, which can be governed by vicinal or more remote heteroatoms. This strategy has some aspects in common with the well-known allylations or aldol condensations to carbonyl derivatives. But in the present case, the C=C bond has a low polarity. We present here some examples which lead to di- or polysubstituted linear substrates, of given geometry, where the organodimetallic obtained has been doubly protonated by water. Further elaborations (to alkenes, ketones, etc.) are possible.

Carbometalation of unactivated alkenes by zinc enolate derivatives

“…As for delocalised organozinc nucleophiles such as allyl-and propargylzinc reagents, vinylmagnesium halides are excellent electrophiles 30,31 towards zincated hydrazones and undergo rapid addition to afford gem-Zn-Mg dimetalated hydrazones (Scheme 13). 32 As exemplified in the case of hydrazone 20, the nucleophilic behavior of these adducts is rich.…”

Carbometallation Reactions

“…Much better yields and selectivities were found in the allylmetallation of various vinyl Grignard reagents. Indeed, very high diastereoselection was obtained during the addition of a vinylzinc bromide to a (Z)-or (E)-vinylmetal reagent, and the results were extensively discussed in several chapters and reviews [3,[146][147][148]. More recent theoretical calculations have led to a better understanding of the reaction [12].…”

Allenylzinc reagents: new trends and synthetic applications

“…The Universite´Pierre et Marie Curie has been deeply involved in such progress through the work of M. Gaudemar [4][5][6][7] and J.-F. Normant. 8,9 Following these research contributions, our team has been largely involved in organozinc chemistry developments. We have particularly focused our research interest on the reactivity of propargyl/allenyl organozinc compounds and their use in stereo-and enantioselective synthesis.…”