Luc Dechoux

Stereospecific substituted alkene synthesis by organo lithium reductive alkylation of epoxides

Abstract Stereospecifically alkylated olefins were synthesized in good yields by reaction of various epoxides with organolithium reagents with concommitant introduction of the alkyl group.

Regiospecific access to cyclic allylic alcohols by reductive alkylation of α-alkyloxy-epoxides

Allylic alcohols are synthesized by treatment of α-alkyloxy-epoxides with organolithium reagents; The reaction proceeds via a carbenoid pathway.

Metalated epoxides as carbenoids. Stereospecific synthesis of functionalized spiro cyclopropanes via highly strained tricyclic intermediates

Abstract Intramolecular cyclopropanation reaction of β-γ-unsaturated epoxides yields highly strained tricyclo[4,1,0,0 1,5 ]heptane compounds whose hydrolysis affords α-keto spiro cyclopropanes. Both steps of this one-pot reaction are stereospecific.

A simple one-pot preparation of (Z)-cyclopropanes from γ,δ-ketoalkenes using KOH/DMSO intramolecular alkylation conditions

Sequential treatment of λ,δ-ketoalkenes with aqueous NBS in DMSO and KOH as solid provides (Z)-cyclopropanes in good overall yields with a diastereoselective excess >;99%.

Asymmetric synthesis of nitrogen heterocycles by reaction of chiral β-enaminocarbonyl substrates with acrylate derivatives

Abstract We have studied the reactivity of β-enaminoesters 1 (R 2 =OMe) or β-enaminoketone 1 (R 2 =Me), derived from ( S )-phenylglycinol, with activated acrylate derivatives. Substrates 1 (R 1 =Me) afforded by aza-annulation oxazololactams 2 and 3,4-dihydro-2-pyridones 3 . In the same conditions β-enaminoesters 1 (R 1 =H) furnish N -acylated oxazolidines 4 .

Acidic isomerization of vicinally substituted (cis)-acceptor-donor cyclopropanes via an open ring mechanism

Many (cis)-cyclopropanes bearing 1-electronwithdrawing and 2-hydroxymethylene groups were synthetised and isomerized under midl acidic conditions to afford the corresponding trans isomers. The mechanism is reported.

Metalated Epoxides as Carbenoids − Further Advances in the Stereospecific Synthesis of Spirocyclopropanes

The intramolecular cyclopropanation of β,γ-unsaturated metalated epoxides derived from 11 yielded the highly strained tricyclic intermediates 7. The facile hydrolysis of the latter species afforded the α-keto spirocyclopropanes 8 in a stereospecific fashion. Indeed, the stereochemistry of the starting alkenes 11d−e governs the relative configuration of the cyclopropanes 8d−e. Furthermore, these spiro systems readily underwent acid-mediated ring opening by various nucleophiles, leading to the substituted enones 12.

Studies Directed Toward the Synthesis of Taxanes: Construction of the Tricyclo[5.3.1.01,7]undecane System

The intramolecular nucleophilic substitution of an epoxide by the anion of a nitrile was used to construct the bicyclo[3.1.0]hexane system of 9, derived from 8, and of 14, derived from 13. The intramolecular 1,3-dipolar cycloaddition of nitrile oxide 4, obtained from 14, led to isoxazoline 3. However, it was not possible to convert 3 into the corresponding β-hydroxy ketone. Rearrangements of 3 were observed in the presence of dehydrating reagents leading to compounds 19–21, which are structurally related to 11(151)abeotaxanes.

Synthesis of enantiopure substituted aziridines by diastereoselective N-bromocyclization and nucleophile-mediated regioselective opening

Abstract Enantiopure β-substituted aziridines were prepared from (S)-phenylglycinol through a key N-bromocyclization of an unsaturated iminoether. A total control of the regioselectivity was observed during the opening of these aziridines by various nucleophiles (N3−, H2O, EtOH, Me2CuLi).

Studies Directed Toward the Synthesis of Taxanes: Evaluation of the B-Ring Formation By an Intramolecular Nitrile Oxide Cycloaddition

Several models for the formation of the 8-membered B-ring of taxanes by an intramolecular nitrile oxide [3+2] cycloaddition were prepared from the monoacetal of 2,2-dimethylcyclohexane-1,3-dione (5). The nitrile oxides were then generated under high-dilution conditions. In most cases only oligomers were obtained. The isoxazoline 19, containing a 9-membered ring, was formed from the nitrile oxide 17, and a bis(isoxazoline) 21was isolated from the reaction of the nitro compound 16c.