Jerome Guillemont

A new prenylation method using the lithium enolate of prenal. Reaction with aldehydes and α,β-unsaturated aldehydes.

Abstract A γ-condensation of the enolate of prenal 1 is observed with aldehydes and α,β-unsaturated aldehydes. In this last case, a conjugate addition is obtained. Intermediate dihydropyrans 4 yield dienals 5 by hydrolysis.

A new prenylation method using the lithium enolate of prenal. Reaction with polyunsaturated aldehydes. A short access to retinal.

Abstract The enolate of prenal 1 prepared from the corresponding silyl enol ether 2 or enol acetate 3 led to a γ-regiospecific reaction with polyunsaturated aldehydes 4 yielding dihydropyrans 5 leading after hydrolysis to polyenals 7 . This process allows the introduction of the isoprenyl skeleton. A synthesis of retinal. from β-ionylidenacetaldehyde is reported.

Aldolisation-type reaction versus Michael-type addition. Hemiacetal vinylogs : versatile synthons

Depending on the steric hindrance of the reaction centers, hemiacetal vinylogs 1 in the presence of BF3.OEt2 can, with enol ethers, lead to a Michael-type addition (4) or an aldolisation-type reaction (3). Hemiacetal vinylog 1b always yields the second reaction leading to β-methoxy-γ,δ-ethylenic carbonyl compounds 4 precursors of polyenic carbonyl compounds 5. Crotonaldehyde and methanol can be used instead of compound 1b.

Bromation des enamines du prénal et du crotonaldéhyde. Voie d'accès aux ω-bromo aldéhydes et ω-bromo acétals correspondants

Abstract Bromination of enamines of prenal and crotonaldehyde yields the corresponding ω-bromoaldehydes via the simple hydrolysis of iminium salts. The carbonyl function of these aldehydes can be protected as acetals or dioxolane. The overall process can be realized in a one pot procedure. The dioxolane is the starting material of a phosphonate which allows,by condensation with β-ionylidenacetaldehyde a direct access to the retinal with a 27.5% overall yield from the enamine 2