Pedro Noheda

Formation of α,β-unsaturated carbonyl compounds by palladium-catalyzed oxidation of allylic alcohols

Treatment of allylic alcohols with catalytic amounts of palladium catalysts in the presence of oxygen leads to the formation of α,β-unsaturated carbonyl compounds.

Reactions of cationic hydrido complexes [Ru(CO)H(MeCN)2(PPh3)2]A (A ClO4, PF6) with alkynes. The crystal structure of [Ru(CO) (MeOOCCCHCOOMe) (MeCN)2(PPh3)2]ClO4

Abstract Reactions of [Ru(CO)H(MeCN)2(PPh3)2]A with mono- and di-substituted acetylenes give the alkenyl derivatives [Ru(CO)(RCCHR′)(MeCN)2(PPh3)2]A (A  ClO4, R  H; R′  C3H7, CMe3, Ph, COOMe; R  R′  COOMe; A  PF6, R  R′  Ph) resulting from a cis-insertion of the alkyne into the RuH bond. The reaction of the perchlorate complex with diphenylacetylene yields alkenyl chlororuthenium derivatives resulting from the unexpected reduction of the perchlorate anion to chloride. The crystal structure of [Ru(CO)(MeOOCCCHCOOMe)(MeCN)2(PPh3)2]ClO4 has been determined by X-ray crystallography (orthorhombic, P212121, a 14.498(1), b 15.080(1), c 22.677(2) A). In this cationic complex both phosphine and acetonitrile molecules and, consequently, the carbonyl and alkenyl ligands are mutually trans, whereas in the other complexes only the phosphine ligands are in trans disposition, as inferred from 1H NMR spectroscopic data.

Synthesis of anthraquinone derivatives by palladium-catalyzed coupling of triflates with stannanes

Abstract The palladium-catalyzed coupling of hydroxyanthraquinone triflates with stannanes provides an efficient entry into substituted anthraquinones under neutral conditions.

Asymmetric catalysis. Asymmetric catalytic intramolocular hydrosilation and hydroacylation

Abstract Catalyst of the type [Rh(chiral Diphosphine)]+ efficiently catalyse the intramolecular hydrosilation of silyl ethers derived from allylic alcohol. The products can be converted to chiral 1,3-dols. High enantiomeric excesses (ees) are observed for substrates bearing an aryl group at the olefin terminus. These same catalyst produce chiral cyclopentanones from 4-substitued 4-pentenals. Tertiary acyl and ester substituents give nearly quantitative ees. The mechanism of hydrosilation is inferred to involve silyl olefing insertion, whereas the key step in hydroacylation probably involves reductive elimination of the metallacyclohexanone intermediate.

Functional and Molecular Characterization of Voltage-Gated Sodium Channels in Uteri from Nonpregnant Rats

Abstract We investigated the function and expression of voltage-gated Na+ channels (VGSC) in the uteri of nonpregnant rats using organ bath techniques, intracellular [Ca2+] fluorescence measurements, and RT-PCR. In longitudinally arranged whole-tissue uterine strips, veratridine, a VGSC activator, caused the rapid appearance of phasic contractions of irregular frequency and amplitude. After 50–60 min in the continuous presence of veratridine, rhythmic contractions of very regular frequency and slightly increasing amplitude occurred and were sustained for up to 12 h. Both the early and late components of the contractile response to veratridine were inhibited in a concentration-dependent manner by tetrodotoxin (TTX). In small strips dissected from the uterine longitudinal smooth muscle layer and loaded with Fura-2, veratridine also caused rhythmic contractions, accompanied by transient increases in [Ca2+]i, which were abolished by treatment with 0.1 μM TTX. Using end-point and real-time quantitative RT-PCR, we detected the presence of the VGSC alpha subunits Scn2a1, Scn3a, Scn5a, and Scn8a in the cDNA from longitudinal muscle. The mRNAs of the auxiliary beta subunits Scbn1b, Scbn2b, Scbn4b, and traces of Scn3b were also present. These data show for the first time that Scn2a1, Scn3a, Scn5a, and Scn8a, as well as all VGSC beta subunits are expressed in the longitudinal smooth muscle layer of the rat myometrium. In addition, our data show that TTX-sensitive VGSC are able to mediate phasic contractions maintained over long periods of time in the uteri of nonpregnant rats.

Polycyclic hydroxyquinones. XXVII. Tautomerism in 1,4-Dihydroxy-9,10-anthraquinone Monoimines. Cycloaddition Reactions of Their 1,4-Anthraquinonoid Tautomers☆

Abstract 1,4-Dihydroxy-9,10-anthraquinone monoimine and differently substituted derivatives thereof ( 6a-i ) have been prepared by ammonolysis of the corresponding 1,4-dihydroxy-9,10-anthraquinones. 1 H- and 13 C-n.m.r. studies show the existence of a rapid tautomeric equilibrium in quinone imines of type 6 . Diels-Alder reaction with the 1,4-anthraquinonoid tautomer of quinone monoimines 6a,e affords ABCD tetracyclic systems related to those existing in anthracyclinones.

Total synthesis of (±)-5-iminodaunomycinone and (±)-4-demethoxy-5-iminodaunomycinone

Abstract The total synthesis of (±)-5-iminodaunomycinone ( 4a ) and (±)-4-demethoxy-5-iminodaunomycinone ( 4b ) has been achieved from the readily available 5-methoxy-1,4-dihydroxy-9,10-anthraquinone ( 5a ) and 1,4-dihydroxy-9,10-anthraquinone ( 5b ), respectively. A short and convenient synthesis of (±)-daunomycinone ( 4c ) has also been achieved by acid hydrolysis of 4a . Short syntheses of 4a (R = OMe, X = NH), 4b (R = H, X = NH) and 4c (R = OMe, X = O) are reported.

Chemo-enzymatic synthesis of chiral cyclic compounds: Efficient kinetic resolution of 2-bromo-2-cyclohexenol

Abstract The kinetic resolution of 2-bromo-2-cyclohexenol has been achieved through enzyme-mediated transesterification in organic solvents, using vinyl acetate as the irreversible acylating agent. The effect of the enzyme and the solvent on the velocity and the enantioselectivity of the transformation has been studied. Also the influences of the size of the carbocyclic ring and the substituent in the 2-position have been briefly examined.