Roger Warin

Synthesis of iminoaziridines from carbodiimides and diazoesters : A new example of transition metal salt catalysed reactions of carbenes

Abstract Alkyl diazoacetates react with N,N′-diisopropylcarbodiimide in the presence of transition metal salts (e.g. copper triflate or rhodium (II) acetate) to give 1-isopropyl-2-alkoxycarbonyl-3- isopropyliminio-aziridine in good yield. The reaction takes place at room temperature without formation of the formal dimer of the carbene (maleate and fumarate).

Butadiene 1,4 polymerization catalysis : II. An nmr study of the structure and dynamics of bis(η3-allylnickel trifluoroacetate) and its significance for the mechanism of the polymerization

Abstract 1 H NMR study of the molecular dynamics of bis(η 3 -allylnickel trifluoroacetate) has revealed not only the important role of the metalanion bond breaking in intra- and inter-molecular rearrangements but also stability of the η 3 -allyl coordination on the NMR time-scale. Implications for the mechanism of butadiene polymerization are discussed, and an interpretation of the control of the cistrans isomer ratio is tentatively proposed.

Guianensine, a zwitterionic alkaloid from strychnos guianensis

The isolation and structural determination of an alkaloid isolated from the stem bark of Strychnos guianensis is described. Elucidation of its structure is based mainly on 1D and 2D NMR studies. The new alkaloid has a zwitterionic asymmetrical bis-indole structure and is named guianensine.

Base-catalysed prototropic rearrangement. Part I. Comparison of the base-catalysed and the metal carbonyl-catalysed isomerisation of allyl ethers

The light-induced isomerisation of allylic ethers in the presence of pentacarbonyliron has been compared with that brought about by a basic heterogeneous catalyst, KNH2–Al2O3. The reaction on the basic catalyst proceeds through the usual cis-mechanism. In contrast, the carbonyliron reaction gives cis- and trans-isomers, in a 1 : 1 ratio in the case of allyl phenyl ether. A π-complex was detected (by n.m.r. spectroscopy) as an intermediate in the reaction. The formation of a catalyst which was particularly active for the thermal isomerisation of olefinic double bonds was detected during the irradiation of pentacarbonyliron in allyl phenyl ether. 3-Propoxycyclohexene was readily isomerised under these conditions, whereas it remained unchanged in the presence of very strong bases. Conformational effects of the ring were observed.

Catalysed prototropic rearrangements. Part II. Metal carbonyl-catalysed isomerization of N-allylamides to prop-2-enyl derivatives

The light-induced isomerization of olefins in the presence of pentacarbonyliron has been applied to nitrogen-containing compounds. Since the catalytic procedure was as effective in polar solvents (such as methanol and acetone) as in hydrocarbons, the isomerization of allylic compounds containing very polar functional groups (such as amides and ureas) into the corresponding propenyl derivatives could be effected in good yields. The reactions are however specific and whereas phenyl N-allylcarbamate was quantitatively isomerized to the expected N-propenylcarbamate, the allyl N-phenyl-ester did not react under the same conditions. As basic catalysts are, in general, not convenient for the isomerization of the titile compounds, the procedure is of preparative interest.

Matadine, a cytotoxic alkaloid from Strychnos gossweileri

Matadine, a new alkaloid, has been isolated from the root bark of Strychnos gossweileri. Elucidation of its structure is mainly based on 1H and 1D NMR studies. Its cytotoxic activity has been tested on cancer cells and normal cells. Matadine is an anhydronium base as serpentine, that exerts also a selective inhibiting activity on B16 melanoma cells while it is less toxic in human 2002 non-cancer cells. This selective activity might be well due , as it seems to be the case for serpentine and alstonine, to a higher affinity of matadine for destabilized single-stranded DNA as mainly present in cancer cells.

An indolinic cryptoalkaloid from Strychnos mattogrossensis

A new indolinic cryptoalkaloid, mattogrossine, has een isolated from the roots and branches of Strychnos mattogrossensis collected near Manaus. Elucidation of its structure is based mainly on 2D NMR studies. Two other indolinic alkaloids were also obtained: strychnobrasiline and 12-hydroxy-11-methoxystrychnobrasiline, and their 13C NMR data are provided.

Copper-catalyzed acetoxylation (hydroacetoxylation) of butadiene: A comparison with the hydrocyanation reaction

Abstract Copper bromide catalyzes the monoaddition of acetic acid to butadiene (and less effectively to substituted conjugated dienes) yielding mixtures of acetoxybutenes. The presence of LiBr as additive is necessary for efficient catalytic activity. The efficiency of the catalyst can be further improved by adding halogenated additives and strong carboxylic acids. In contrast, complexing ligands (e.g., PPh 3 polyethers) inhibit the catalyst activity. When compared with the copper-catalyzed hydrocyanation of butadiene, the regioselectivity of the acetoxylation is low, easy interconversion of the linear and branched isomeric products being achieved under the reaction conditions, the 1,4-isomer corresponding to the thermodynamically controlled one.

Venecurine, an indole alkaloid from curare

A new quaternary indole alkaloid, venecurine, has been isolated by chromatographie techniques from a curare obtained from the Hoti tribe of Venezuela. Elucidation of its structure is based mainly on 2D-NMR studies.

Catalysed prototropic rearrangements. Part 3. Metal carbonyl-catalysed isomerization of N-allylsulphonamides to N-prop-2-enyl and N-propylidene derivatives

N-Allylsulphonamides (4) are readily isomerized in the presence of pentacarbonyliron upon irradiation by u.v. light. N-Prop-2-enyl derivatives (5) are obtained, and further isomerization under suitable conditions leads to N-propylidenesulphonamides (6). The last reaction proceeds by a specific 1,3-proton migration involving an N–H group as shown by isotopic labelling experiments.