Michel Bortolussi

2,5-Dihydropyrrole derivatives as enantiomerically enriched building blocks: Synthesis of the Geissman-Waiss lactone and polyhydroxylated pyrrolidines

Abstract Starting from enantiomerically pure 2,5-dihydropyrroles substituted at 2-position, efficient stereoselective syntheses of the (+)-Geissman-Waiss lactone and of (+)-1,4,5-trideoxy-1,4-imino-D-ribo-hexitol hydrochloride have been achieved. This work illustrates the high potential of 2,5-dihydropyrroles for the obtention of polyhydroxylated nitrogen heterocycles.

Stereocontrolled reactions induced by a thermolabile group. Synthesis of optically active 1,3-diols.

Abstract Wittig Horner-Michael reactions of phosphonates with optically active lactol 1 lead preferentially to one diastereoisomer. 2 . Force field calculations conducted on one pair of diastereoisomers 2c and 2′c predict that these isomers must exist in different conformations of similar energies. 1 H NMR data are in good agreement with these predictions. The dihydrofurans obtained by retro Diels-Alder reactions of 2 are easily transformed into optically pure 1,3-diols, precursors of R-(+)-α-lipoic acid and (−)-(1R,3R,5s)- 1,3-dimethyl −2,9-dioxabicylco [3.3.1]nonane.

Stereoselective additions of grignard reagents to masked imines and iminium ions

Abstract Additions of organomagnesium bromides to the masked imine 2 or iminium ion 3 were found to be highly diastereoselective, and were shown to occur on the same diastereotopic face of the CN bonds of these two compounds. Thermolysis of the aminoalcohols obtained gave rise to chiral allylic aminoalcohols of high synthetic potential.

A NOVEL SYNTHESIS OF 2,5-DIHYDROPYRROLE DERIVATIVES AS ENANTIOMERICALLY ENRICHED BUILDING BLOCKS

Abstract A general synthesis of optically active 2,5-dihydropyrroles (3-pyrrolines) substituted at the 2-position by a functionalized chain is described. A highly stereoselective intramolecular Michael reaction afforded the five-membered nitrogen rings with an excellent enantiomeric purity. The unsaturation was generated by a retro Diels-Alder reaction.

Synthesis and rearrangement of (Z)-allylic trichloroacetimidates

Abstract An efficient synthesis of (Z)-allylic trichloroacetimidates starting from lactol 1 is described. Thermal [3,3] rearrangement of these imidates occurred with excellent chirality transfer to give allylic amides.

Reformatsky Reaction Using Zn/Ag Couple

Abstract The Reformatsky reaction is easy to run in ethereal solvents in the presence of Zn/Ag couple. From methyl γ-bromocrotonate and ketones, ramified esters are formed in refluxing Et20, linear ones in refluxing THF.

Dealkoxycarbonylations of Gem Diesters and β-Ketoesters via an Enzyme Catalyzed Hydrolysis

Abstract A new method for the dealkoxycarbonylation of malonate esters and β-ketoesters, involving an enzyme catalyzed hydrolysis followed by a high temperature Kugelroher distillation, is described.

Enantioselective synthesis of lyxo -(2 R ,3 R ,4 R )-C 18 -phytosphingosine using double stereodifferentiation 1

Abstract lyxo -C 18 -Phytosphingosine can be synthesized by the cis -dihydroxylation of an ( E )-allylic trichloroacetamide obtained by an Overman rearrangement. A double stereodifferentiation using AD-mix-β and an enantiomerically enriched ( S )-allylic trichloroacetamide allowed the first synthesis of lyxo -(2 R ,3 R ,4 R )-C 18 -phytosphingosine with high diastereoselectivity (de=94%) and excellent enantioselectivity (ee=93%). This sphingosine was fully characterized by the physical and spectral data of the corresponding tetraacetate.

Flash thermolysis of trimethylsilyl 2-oxobicyclo[3.3.1]nonane-1-carboxylate: formation of a strained bridgehead enol ether

Flash thermolysis of the trimethylsilyl ester (1) gives rise to enol ethers (3) and (5) whose formation is best explained via the strained bridgehead enol ether (2).