The chemistry of pyrazine and its derivatives. XII. The reaction of acetonylpyrazine with phenyllithium in the presence and absence of methyl benzoate

The reaction of acetonylpyrazine with phenyllithium in the absence and presence of methyl benzoate gives (a) 2-phenyl-6-acetonylpyrazine (IV) and (b) a mixture of IV and 3-(2-phenyl-6-pyrazyl)-4-phenylbutane-2, 4-dione (V, VI), respectively. Evidence in support of the structures of the products has been presented and comments on their formation are made.     

Stereospecific carbon-carbon bond formation by the reaction of a chiral episelenonium ion with aromatic compounds

The stereospecific exchange of a hydroxyl group of chiral alcohols bearing a pyridylseleno group on the adjacent carbon atom with aromatic compounds occurred smoothly in the presence of Lewis acid.     

The stoichiometric hydrogenation of 1,1-diphenylethylene with hydridocobalt tetracarbonyl; differences from the hydroformylation reaction

The kinetics of the stoichiometric hydrogenation of 1,1-diphenylethylene with HCo(CO)₄ is cleanly second order, permitting a determination of the activation parameters. The rate is unaffected by the atmosphere over the reaction and is enhanced by substituting DCo(CO)₄ for HCo(CO)₄. These results contrast sharply with those secured in the hydroformylation of 1-alkenes and thus dual mechanistic pathways are available for the reaction of HCo(CO)₄ with unsaturated systems. It is very possible that the stoichiometric hydrogenation of 1,1-diphenylethylene involves a geminate free radical pair but definitive proof is still lacking.     

The formation of a metallacycloheptadienyl intermediate in the reaction of palladacyclopentadienyl derivatives with tetracyanoethylene

The palladium(II) derivatives of the type 1 [Pd(LL′)(C₄R₁R₂R₃R₄)] (LL′ = HNSPh:2-(phenylthiomethyl)-pyridine (A), BiPy: 2,2′-bipyridyl (B), DPPE: bis-diphenylphosphinoethane (C), NEOC: neocuproine (2,2′-dimethyl-o-phenanthroline) (D), R₁ = R₄ = COOMe, R₂, R₃ = C₁₀H₆ (a), R₁ = R₃ = C₆H₅, R₂ = R₄ = COOMe (b), R₁ = R₂ = R₃ = R₄ = COOMe (c)) react with the electron poor olefin tetracyanoethylene (TCNE) to yield under mild conditions the type 2 cycles C₆(CN)₄R₁R₂R₃R₄ and the corresponding palladium(0) olefin derivative [Pd(η²]-TCNE)(LL′)]. The olefin insertion reactions are usually fast, but in the case of the reaction of complex 1Da with TCNE accumulation of an intermediate is observed. The low temperature NOESY spectrum allows the determination of the intermediate structure which can be described as a hepta-membered metallacycle species.     

The lack of intramolecular carbonyl ligand rearrangement in the stereospecifically 13co labelled (diamine)molybdenum tetracarbonyl derivatives

The preparation and spectral characterization of stereospecifically, axially labelled Mo(CO)₃(¹³CO)(diamine) complexes (diamine  N,N,N′,N′-tetramethylethylenediamine and N,N,N′,N′-tetramethyl-1,3-diaminopropane) and the rigidity (or lack of fluxionality) of the carbonyl ligands during subsequent thermal reactions of these derivatives are reported.     

Regioselective synthesis of trisubstituted 2,3-dihydrofurans from donor-acceptor cyclopropanes or from reaction of the Corey ylide with alpha-sulfenyl-, alpha-sulfinyl-, or alpha-sulfonylenones

[reactions: see text] Regioselective synthesis of 2,4,5- or 3,4,5-trisubstituted 2,3-dihydrofurans has been realized by using donor-acceptor cyclopropanes or by a Corey ylide reaction with alpha-sulfenyl-, alpha-sulfinyl-, or alpha-sulfonylenones. The method allowed a straightforward synthesis of the natural product calyxolane B.     

Reactions of coordinated molecules XI. The reaction of the rhenium tetracarbonyl metallo-acetylacetone complex with hydrazines

The reaction of the rhenium tetracarbonyl metallo-acetylacetone molecule, cis-(OC)₄Re[C(CH₃)OHO(CH₃)C], with hydrazine, methylhydrazine and phenylhydrazine affords the corresponding acetyl-amine complexes, cis-(OC)₄- Re(COCH₃)(NH₂R), where R = H, CH₃, or C₆H₅, and acetonitrile. The reactions were followed by proton NMR at 36°C. The half-lilfe of the reaction with phenylhydrazine was 8.67 minutes while the other two hydrazines gave complete reaction within 30 seconds. The X-ray molecular structure determination of the acetyl-aniline complex is reported.     

Studies on the reactions of silyl enol ether with perfluoroorganic compounds I. The reaction of silyl enol ether with perfluoroalkyl iodide

The reaction of silyl enol ethers ( 1a-1e ) with perfluoroalkyl iodides ( 2f–2k ) initiated with sodium dithionite was studied. α-Perfluoroalkyl ketones (3) were synthesized in excellent yield by this method. α, β-Unsaturated fluorinated ketones (4) were obtained easily by dehydrofluorination of the α-perfluoroalkyl ketones. A radical mechanism was proposed.     

Intermediate carbene formation in the reaction of thioamides with phosphorus (III) derivatives: Quantum chemical investigation

The reactions of perfluoroalkyl thioamides with trimethyl phosphine, trimethyl phosphite, and tris(dimethylamino)phosphine have been analyzed by means of quantum chemical (DFT and MP2) calculations. The reaction seems to proceed via the nucleophilic attack of the electrophilic carbon atom by the phosphorus lone pair with the formation of cyclic or acyclic adducts. The latter releases the thiophosphate molecule forming perfluoroalkylaminocarbene as the short‐lived intermediate. The reaction of the carbene with the second molecule of trialkyl phosphite yields phosphorus ylide. The ylide undergoes a migration of fluorine from carbon to phosphorus. The reactions of perfluoroalkyl thioamides with phosphines and tris(dimethylamino)phosphine probably proceeds differently. Using alkyl thioamides or amides instead of perfluoroalkyl thioamides also makes the reaction less favorable. The only combination of perfluoroalkyl thioamides with trialkyl phosphite fulfills both the kinetic requirements (moderate activation energies and relative energies for intermediates) and the thermodynamic aspects (higher stabilities of the reaction products compared with the starting materials). © 2013 Wiley Periodicals, Inc.     

The reaction of 1-silylcyclopropyl anions with dichloromethyl methyl ether: the efficient synthesis of cyclopropyl silyl ketones via cyclopropylidene derivatives

The reaction of 1-silylcyclopropyl anions with dichloromethyl methyl ether is described. The reaction with an excess amount of dichloromethyl methyl ether gives the corresponding cyclopropyl silyl ketones in low yields. On the other hand, the reaction under basic conditions proceeded smoothly to afford the corresponding cyclopropylidene derivatives, exclusively. The resulting cyclopropylidene compounds are subjected to hydrolysis or trapping with electrophiles easily to give the cyclopropyl silyl ketone derivatives in good yields.     

The palladium-catalyzed reaction of aryl iodides with mono and disubstituted acetylenes: a new synthesis of trisubstituted alkenes.

Mono and disubstituted acetylenes react with aryl iodides containing a variety of functional groups in the presence of palladium catalyst, formic acid and a tertiary amine to give trisubstituted alkenes.     

Asymmetric hydrogenation of trisubstituted olefins with iridium-phosphine thiazole complexes: a further investigation of the ligand structure

New chiral bidentate phoshine thiazoles have been prepared and successfully applied as ligands in the homogeneous iridium-catalyzed asymmetric hydrogenation of aryl alkenes and aryl alkene esters. The ligands are designed to be highly modular and have one common chiral intermediate, from which diversity can be introduced at a late stage in the synthetic pathway. It was found that a six-member-ring backbone of the rigid ligand structure was preferred over seven- or five-member rings. In this study it is shown that the substituent pattern of the ligands has a major influence on the stereochemical outcome of the products. By applying the selectivity model proposed in this study, it is possible to match different substrates against different catalysts. In this way, good to excellent enantioselectivity can be obtained for typically difficult substrates. Geometrically different derivatives of alpha- and beta-methyl cinnamic acid ethyl esters were hydrogenated, to demonstrate the validity of the selectivity model and to verify the importance of steric and electronic matching of the catalyst and the substrate.