Jesús H. Rodríguez

Stereochemistry of organic sulphur compounds. part 13. Configurational assignment of diastereoisomers of 2-methylsulphinyl-1,2-diphenylethanol and of their O-methyl and O-acetyl derivatives

Abstract The synthesis, isolation and conformational analysis of the diastereomeric 2-methylsulphinyl-1,2-diphenylethanol and of its O -methyl and O -acetyl derivatives are reported. Chemical correlations and the study of the influence of solvent polarity changes on the coupling constants have permitted the configurational assignment. Lanthanide shift reagents have been used also. to this effect. The role of hydrogen bonding in the hydroxysulphoxides has been evaluated in diluted solutions by IR and NMR spectroscopy. A donor-acceptor interaction between oxygen and sulphur has been invoked to explain the differences in conformational behaviour between epimeric sulphoxides at sulphur atom.

Short and efficient enantioselective synthesis of cis and trans pyrrolidine-2,5 dicarboxylic acids

Abstract N-BOC-ethyl pyroglutamate 1 undergoes nucleophilic ring opening with lithium methyl p-tolyl sulfinyl anion delivering the p-tolylketosulfoxide 2. Treatment of 2 with TFA gave rise to a mixture of thioesters 3a,3b. The hydrolysis of 3b afforded (2S, 5S) pirrolidine-2,5 dicarboxylic acid 5, a constituent of the red Alga Schizymenia dubyi . Under Pummerer reaction conditions (TFAA/Pyr), 2 yielded the 5-oxo-L-pipecolic acid derivative 6.

Reactions of chiral β-ketosulfoxides with Et2AlCN: Asymmetric synthesis of cyanohydrin derivatives.

Abstract The reaction of chiral p -tolylsulfinylmethyl ketones (R-CO-CH 2 -SOTol, RPh, Et and t -Bu) with Et 2 AlCN, yields almost optically pure sulfinyl cyanohydrins (d.e. ≥ 96%). The reaction was quicker in the presence of ZnCl 2 , but the stereochemical results were identical, The cyanohydrins were transformed into the α-methyl α-hydroxyamides (e.e.-92%) by hydrolysis of the CN group and subsequent hydrogenolysis of the CS bond.

Synthesis and stereoselective reductions of chiral β-iminosulfoxides

Abstract Reaction of chiral non racemic β-ketosulfoxides with amines or condensation of the imine enolates with (−)-methyl sulfinate yield optically pure β-iminosulfoxides. The second method requires the presence of an excess of MgBr 2 in order to avoid epimerization at sulfur. The highly diastereoselective reduction of these substrates can be successfully achieved only with DIBAL/ZnBr 2 (d.e.97%). Hydrogenolysis of the CS bond on the obtained β-aminosulfoxides yields the protected with e.e. higher than 97%.

Reactivity of acetate-bridged cyclopalladated complexes. 1H and 13C NMR studies of some monomeric derivatives of N-(4-methoxyphenyl)-α-benzoylbenzylideneamine

Abstract The reactions have been studied of acetate-bridged cyclopalladated complexes with different reagents to yield monomeric structures. The relative reactivity is even higher than that of the corresponding chloro- and bromo-dimers, usually obtained from the acetates and used as starting materials in bridge-cleavage reactions. The 1H and 13C NMR spectra of the monomeric complexes have allowed evaluation of the influence of the palladium on the chemical shifts of the surrounding nuclei. The slow crystallization of [{Pd(μ-Br)(4-MeOC6N4NC(COC6H5)C6H4)}2] from DMSO induces a bridge-splitting reaction to afford [Pd(4-MeOC6N4NC(COC6H5)C6H4)(DMSO)Br].

Stereochemistry of organic sulphur compounds : Part. 17 conformational analysis of some erythro- and threo-thio-derivatives of β-fluorinated and β-oxygenated ethanes

Abstract The synthesis and conformational analysis of 2-fluoro, 2-hydroxy and 2-methoxy thioderivatives (thioethers, sulphoxides, sulphones and sulphonium salts) of 1,2-dimethyl and 1,2-diphenylethanes ( erythro and threo ) are reported. Steric effects in thioethers and electrostatic interactions in sulphonium salts are the main factors determining the stability rotamers. A balance of these factors controls the conformational equilibria in sulphoxides and sulphones. Electronic interactions between the π -aromatic electrons or the unshared β-heteroatomic electrons and the sulphur atom are suggested to explain large differences in rotamer populations induced by changes in the carbon sketelon or in the relative configuration of the sulphinylic sulphur.

Reaction of folded acetate-bridged ortho-palladated complexes with CH2Cl2. Crystal structure of[{Pd(C6H5 CH2 N C (COC6H5) C6H4)(μ-Cl)}2]

Abstract Folded acetate-bridged ortho -palladated complexes of benzoylbenzylideneamines react with CH 2 Cl 2 to afford unfolded chlorobridged ortho -palladated complexes. This finding is supported by an X-ray crystallographic study of the complex [{Pd(C 6 H 5 CH 2  NC(COC 6 H 5 )C 6 H 4 )(μ-Cl)} 2 ].

Basic media behavior of N-[2-(1-hydroxy-2-Y-ethyl)phenyl] ethyl carbamates (Y = SMe, SOMe, SO2Me, H, Br, CN)

Abstract From the results obtained in the hydrolysis reaction of the carbamate group of some thioderivatives compounds whose common structure is (2 → tOOCNH-C6H4)-CHOH-CH2Y a mechanism is suggested to explain the products, as well as the relationship between the relative configuration of diastereoisomeric sulfoxides (Y = SOMe) with the reaction rate and with the stereochemical outcome. Other interesting and unexpected products are yielded when the hydrolysis reaction of others carbamates (Y = H, Br, CN) is carried out In the present cases, the carbamate functioh seems to behave as a very versatile group capable of readily undergoing conversions to several Kinds of heterocycles.

Synthesis and conformational analysis of some oxisuran metabolites and their o-methylderivatives

Abstract The synthesis is given of oxisuran (methylsulphinyl methyl-2-pyridyl ketone) and its metabolites and derivatives, whose structures are 2-Py-CO-CH2-SOxCH3 ( X=0,1,2) and 2-Py-CHOR-CH2-SOnCH3(R=H, Me; n=0,1,2). From the results obtained in the reaction of oxisuran with different reducing agents, a new stereochemical pathway is suggested to explain the stereoselectivity observed in the reduction of β-keto-sulphoxides with DIBAL. The conformational analysis of hydroxy and methoxyderivatives is discussed in relation with that previously reported for 2-thioderivatives of 1-phenylethanol and their O-methylderivatives. The configurational assignment of diastereoisomeric sulphoxides is made on the basis of their different conformational behaviour, confirming the assignment deduced from the stereoselectivity observed in the reduction of oxisuran.

Synthesis and hydride reductions of chiral cyclic β-iminosulfoxides

Abstract The hydride reductions of chiral N-(2-p-tolylsulfinyl)cyclohexylidene phenyl amines 3A and 3B (epimers at C-2), and of N-1-(2-p-tolylsulfinyl)cyclohexenyl benzyl amine, 4, are highly stereoselective, yielding only the corresponding cis-aminosulfoxides.