Ilane Marek

Diastereoselective syn or anti opening of propargylic epoxides. Synthesis of α-allenic alcohols

Abstract Propargylic epoxides easily react with Grignard reagents and catalytic amounts of copper(I) salt to afford α-allenic alcohols. The reaction is highly diastereoselective and its stereochemical outcome ( syn or anti isomer) can be fully controlled. The syn diastereomer, probably arising through an addition-elimination mechanism, is better obtained with RMgCl and copper(I) bromide, whereas the anti diastereomer, is better obtained with RMgBr and a complexed copper(I) salt. With RLi and a catalytic amount of copper salt, phenethynyl cyclohexene oxide reacts through reductive lithition, affording, stereoselectivety, an allenyl lithium reagent.

Zinca-ene-allene and zinc-enolate cyclization. Towards the synthesis of polysubstituted pyrrolidines

Abstract The synthesis of polysubstituted pyrrolidines can be easily achieved in a diastereoselective and enantioselective way via the zinca-ene-allene and zinc-enolate cyclization.

Are allenes formed from propargylic ethers through a syn or anti displacement

Abstract The copper catalyzed reaction of Grignard reagents with asymetric propargylic ethers leads to chiral allenes, with very high optical yield. This reaction proceeds through a syn addition to the triple bond followed by a syn or anti β-elimination, according to the nature of the halogen of the Grignard derivative.

Enantioselective Carbolithiation of β-Alkylated Styrene

Abstract Stoichiometric or catalytic amounts of (−) sparteine serve as promoter for enantioselective carbolithiation of β-alkylated, non functionalized styrene.

Iodocyclization of olefinic t-butyl ethers : an easy stereocontrolled synthesis of cis-substituted tetrahydrofurans.

Abstract The iodoalkoxylation of δ,ϵ olefinic t-butyl ethers leads, with a very high selectivity, to cis substituted tetrahydrofurans.

Diastereoselective synthesis of heterosubstituted organogembismetallic reagents. Application to a new propargylmetalation reaction of vinyl metals

Abstract The allylzincation and propargylzincation of various γ-heterosubstituted vinyl metals proceed diastereoselectively. This represents a new synthetic approach to construct two or three adjacent stereogenic centers in acyclic systems.

Stereoselective synthesis of linear and angular triquinanes skeletons via the zinca-ene-allene reactions

Abstract The zinca-ene-allene reaction allows a new diastereoselective and straightforward alternative to the angular and linear triquinane framework synthesis.

Metal-alkene π-chelation: A stereodirecting effect in allylzincation reactions and in zinc mediated cyclopropanations

Abstract A π-chelation between an olefinic site and a zinc atom γ to this unsaturation governs the allylzincation reactions and 1,3-elimination reactions from organogembismetallic reagents.

Diastereoselective synthesis of α-allenic alcohols from propargylic epoxides

The cuprocatalyzed reaction of a Grignard reagent with propargylic epoxides proceed through an addition-elimination mechanism. By changing the reaction conditions, particularly the halogen atom of RMgX it is possible to control the diastereoselectivity of the reaction. Both diastereoisomers of anf allenic alcohol can thus be obtained at will.

Intramolecular carbometallation of organozinc reagents.

Abstract The intramolecular cyclization reaction of primary or secondary alkenylzincs leads to a cyclopentylmethylzinc derivatives in a totally regiospecific 5-exo-trig cyclization in the presence of a highly sensitive function.