Cirilo García-Martínez

RING CURRENT EFFECTS OF PHENYL AND NAPHTHYL GROUPS : INTERNAL PROBES FOR DETERMINING THE ABSOLUTE CONFIGURATION OF CHIRAL AZETIDIN-2-ONES BY 1H NMR

Abstract The ring current effects of the phenyl and 1-naphthyl rings are used to determine the absolute configuration of ten chiral azetidinones prepared from the [2+2] cycloaddition of (S)-1-(1-naphthyl)ethyl and (S)-1-phenylethyl isocyanate to vinyl ethers under high pressure. The (S)-1-arylethyl group of the studied azetidinones adopts a preferred conformation that can be distinguished by 1 H NMR spectroscopy. The application of this principle to other azetidinones containing the arylethyl substituent is consistent with the configurations determined by chemical correlation and X-ray diffraction and verifies the reliability of the proposed method.

Synthèse formelle de la (±)-physostigmine

Abstract The synthesis of 3-cyanomethyl-1,3-dimethyl-5-methoxyindol-2-one 2 , a precursor for physostigmine 1 , was achieved from ethyl 2-cyano-2-(1-carboethoxy-5-methoxy-3-indolyl)acetate 3a .

Configurational 1H NMR study of optically active 7-(1-phenylethyl)-2-oxa-7-azabicyclo[3.2.0]heptan-6-one derivatives using Pirkle’s alcohols and a chiral shift reagent

Four novel stereoisomers of 7‐(1‐phenylethyl)‐2‐oxa‐7‐azabicyclo[3.2.0]heptan‐6‐one were prepared under high pressure from [2+2] cycloaddition of the pure enantiomers of 1‐phenylethyl isocyanate and 2,3‐dihydrofuran. Their conformational preferences in solution and the absolute configurations of the bridgehead carbon atoms were unambiguously determined by 1H NMR spectroscopy using tris[3‐(2,2,2‐trifluoro‐1‐hydroxyethylidene)‐d‐camphorato]europium(III) and (R)‐ or (S)‐1‐(9‐anthryl)‐2,2,2‐trifluoroethanol (Pirkle’s alcohols). MM2 single‐point energy calculations were consistent with the experimentally determined stereochemistry. ©1998 John Wiley & Sons, Ltd.

Synthesis and 1H and 13C nuclear magnetic resonance of 16-methylene-17α-hydroxypregna-1,4,9(11)-triene-3,20-dione

A three-step synthesis of 16-methylene-17 alpha-hydroxypregna-1,4,9(11)- triene-3,20-dione, which has been previously obtained by microbial transformation, was achieved from 3 beta-hydroxy-16 alpha, 17-epoxy-16 beta-methyl-5 alpha-pregn-9(11)-en-20-one in an overall yield of 35%. All compounds involved in the process were characterized spectroscopically and their 13C NMR shielding effects are briefly discussed.

Further Nuclear Magnetic Resonance Studies of Flavone

The incorporation of 92.7% of 13C at the carbonyl group of flavone allowed to measure two- and three-bond carbon-carbon coupling constants which range from 1.4 to 3.5 Hz, and to measure two-, three- and four-bond carbon-hydrogen coupling constants which range from 0.3 to 3.8 Hz. A mixture of unlabelled flavone 1 with its 4-13C labelled analogue 2 further allowed to measure one-bond induced isotope shifts of -15.5 and -16.2 ppb for C-3 and C-4a, respectively, and a three bond induced isotope shift of

Stereocontrolled Synthesis of 3-Alkylindolines from (Z)-2-Hydroxyindolenines

SummaryA convenient process for the synthesis of 3-alkylindolines2 and their transformation intocis-fused tricyclic γ-lactones3 from allylic alcohols1, mediated by aGrignard reagent, is described. This process proceeds with high stereocontrol at the two newly formed contiguous stereogenic centres. By oxidation with chromium oxide, 2-oxindole derivatives4 are obtained from 3-alkylindolines2.ZusammenfassungEine einfache Methode zur Herstellung der 3-Alkylindoline2 und deren Umsetzung zu dencis-kondensierten tricyclischen γ-Lactonen3 aus den Allylalkoholen1 mittels einerGrignard-Verbindung wird beschrieben. Die Reaktion verläuft unter hoher Stereoselektivität bezüglich der zwei neu gebildeten Asymmetriezentren. Durch Oxidation mit Chromtrioxid erhält man aus den 3-Alkylindolinen2 die 2-Oxindolderivate4.