P. Cadiot

Boronates allyliques, alleniques et propargyliques: Preparations et proprietes

Abstract An easy synthesis of linear cyclic 2-unsaturated boronates via organometallic reagents has been achieved. The final structure of the carbon framework is related to the tetracoordinated intermediate. Intermolecular rearrangement, disproportionation and reactions with carbonyl compounds have been studied.

Insetion d'allenes: VIII. Formation de cetones α,β insaturees par hydroacylation d'allenes en presence de tetracarbonyl ferrate de sodium☆

Abstract α,β-Unsaturaated ketones are generated in moderate yields (50–60%) from allene or a mono-, di- or tri-substituted allenic hydrocarbon, n alkyl halide and sodium tetracarbonylferrate. The first step is the formation of a complex anion which results from transfer of the alkyl group on a coordinated CO, then of the acyl ligand thus formed on the allenic sp carbon. Protonation with acetic acid yields a hydroxy-η 4 -trimethylenemethane, easily isomerized into an η 4 -heterodieneiron tricarbonyl. Finally, the α, β-unsaturated ketone is released upon oxidation with trimethylamine oxide. The most substituted ketone predominates.

Insertion d'allenes : II. Cyclisation d'halogénures éthyléniques et alléniques avec le tétracarbonylferrate de sodium (Fe(CO)42-, 2 Na+. Formation de cétones cycliques☆

Abstract The cyclisation of previously described ω-unsaturated η 1 -alkyl ligands has been extended using the versatile Fe(CO) 4 metallic fragment. Treatment of the homoallenic halide 5-bromo-1,2-pentadiene with disodium tetracarbonylferrate (Fe(CO) 4 2- , 2 Na + gives, after protonation, 2-methylcyclopentenone in 30–40% yield. The structure and reactivity of the reaction intermediate, subsequent to the cyclisation step, suggest delocalisation of electronic density onto the organic ligand. The metallic reagent converts some alkenyl halides into cyclic ketones in low to moderate yields.

Insertion d'allenes

Abstract η 3 -Allylcyclopentenone complexes of molybdenum and tungsten are obtained by treating homoallenic bromides with η 5 -cyclopentadienyl-molybdenum or -tungsten tricarbonyl anions. Conformational equilibria were observed and studied by NMR. The results can be explained by assuming that the dominant factor is a steric interaction between the cyclopentadienyl ring and the substituents on the η 3 -allyl ligand. According to the NMR data one of the compounds was in a B exo conformation. This conclusion was asserted by an independent study using X-ray diffraction techniques.

Insertion d'allenes: VII. Synthese de complexes (η4-heterodiene)fer tricarbonyl a partir d'allenes

Abstract η 4 -Hydroxytrimethylenemethaneiron complexes are obtained by protonation of complex anions. They isomerise easily into a mixture of isomeric η 4 -heterodieneiron tricarbonyl complexes which have been separated. This demonstrates that such complexes are now available starting from allenes, alkyl halides and sodium tetracarbonyl ferrate.

Insertion d'allenes : V. Complexes anioniques resultant de l'insertion d'allenes dans une liaison feracyle. delocalisation de la charge negative et formation de paires d'ions

Abstract Insertions of allenes into ironacyl bonds proceed readily and quite efficiently. When the reaction product is neutral an η 3 -allyl ligand is generated, but not when the product is an anion. Transfer of electronic density to the organic ligand is shown to occur. This is reflected in ion pairing phenomena which are studied by monitoring the change in v (CO) and v (Cz.dbnd;O) in the IR as a function of the solvent and/or the counter ion. The oxygen of the ligand oxo group is the site of interaction with the cation Na + .

Nouveaux complexes de structure η4-trimethylenemethane obtenus a partir du tetracarbonylferrate de sodium par insertion d'allene dans une liaison metalcarbone

Abstract The mechanism of formation of α,β-unsaturated ketones in the reaction of disodium tetracarbonylferrate, with an alkyl bromide and allene, is investigated; new intermediate complexes are isolated. In the anion resulting from insertion of allene into an ironacyl bond the negative charge is delocalised over the metallic center and the organic ligand and confirms an η 4 -trimethylenemethane type behaviour. Reactions with (CH 3 ) 3 SiCl and proton yield neutral η 4 -trimethylenemethane complex. In the case of proton a subsequent sigmatropic shift yields a η 4 -heterodiene complexe. The anion is isolated as its ionic cristalline PPN + salt.

Alcoxycarbonylation : III. Complexes η3-allyliques du molybdene; equilibres conformationnels et effets steriques☆

Abstract Diastereoisomers and conformers of η3-allylmolybdenum phosphine or phosphited complexes have been identified by NMR spectroscopy. The most stable conformation (A endo or B exo) are those which minimize the steric interaction between the allyl substituents and the phosphorus-containing ligand. The largest coupling constants are between the phosphorus and hydrogen atoms in the cis position.

Alcoxycarbonylation : II. Alcoxycarbonylation de complexes σ-propargyliques du molybdene coordines par une phosphine

Abstract Synthesis and stereochemistry of σ-propargylic molybdenum complexes coordinated by a phosphine or a phosphite ligand are described. These complexes are alkoxycarbonylated by alcohols and thiols to yield π-allyl complexes. An acid catalysis is observed and a reaction scheme suggested. The complexes with a chiral π-allyl ligand are obtained as a mixture of two diastereoisomers which are separated.

Insertion d'allene dans une liaison fer-acyle. Formation de cetones α,β-insaturees a partir du tetracarbonyl ferrate de sodium

Abstract Disodium tetracarbonylferrate(−II) reacts with alkyl bromides and allene to yield α,β-unsaturated ketones. It is suggested that the reaction proceeds through insertion of “allene” into an ironacyl bond to yield an anionic intermediate which gives a π-heterobutadiene complex after protonation. Oxydation with trimethylamine oxide ultimately yields the ketone.