Synthèse et étude conformationnelle de dioxa-1,3 aza-9 spiro[5,5]undecanes

Synthesis of the new l,3-dioxa-9-azaspiro[5.5]undecane ring, was realized by the scheme represented in Figure 2. Butyro-phenones 6 posses neuroleptic activity similar to that of halo-peridol. The pharmacological activity was reported in another publication (2). Conformational study of l,3-dioxa-9-azaspiro-[5.5]undecanes shows the existence of four conformations A, B, C and D, which are shown in Figure 4. The existence of these conformations depends on the nature of the substituents R and R' on the dioxane ring. Thus, in the compounds where R ≠ H, R' = H, the four conformations are possible with a preponderance of A and B. If R and R' are different from H only the conformation A is present in 99% concentration. Lastly, when R = R' = H, the four conformations are possible with equal population for the couple A, B and the couple C, D; the first couple predominating. The presence of a fluorophenylbutyric moiety on the piperidine nitrogen does not seem to stereochemically modify the heterocyclic group.     

A general organocatalyst for direct alpha-functionalization of aldehydes: stereoselective C-C, C-N, C-F, C-Br, and C-S bond-forming reactions. Scope and mechanistic insights

The development of a general organocatalyst for the alpha-functionalization of aldehydes, via an enamine intermediate, is presented. Based on optically active alpha,alpha-diarylprolinol silyl ethers, the scope and applications of this catalyst for the stereogenic formation of C-C, C-N, C-F, C-Br, and C-S bonds are outlined. The reactions all proceed in good to high yields and with excellent enantioselectivities. Furthermore, we will present mechanistic insight into the reaction course applying nonlinear effect studies, kinetic resolution, and computational investigations leading to an understanding of the properties of the alpha,alpha-diarylprolinol silyl ether catalysts.     

Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes

The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed.     

Ouverture d'epoxydes par des acides organiques dans L'H.M.P.T.: nouvelle voie d'acces a des desoxypentopyranosides

The opening of pyranic epoxides with organic acids in HMPA leads to regioselectively esterified methyl deoxy$\text{threo}$pentopyranosides; one of them is a convenient intermediate to provide $\text{erythro}$ isomers.     

Sur la propriétéP *

On the PropertyP _*. LetG be a locally compact group. We give a direct proof of the equivalence of the propertiesP ₁ andP _*, avoiding the use of invariant means onL (G).     

Organocatalytic asymmetric alpha-bromination of aldehydes and ketones

The first organocatalytic enantioselective alpha-bromination of aldehydes and ketones is presented; a C2-symmetric diphenylpyrrolidine catalyst afforded the alpha-brominated aldehydes in good yields and up to 96% ee, while ketones were alpha-brominated by a C2-symmetric imidazolidine in up to 94% ee; furthermore, the organocatalytic enantioselective alpha-iodination of aldehydes is also demonstrated to proceed with up to 89% ee.