Cycloaddition d'ylures d'azométhine dérivés de la 3,4-dihydro-6,7-diméthoxy-3-méthoxycarbonyl-isoquinoléine

Three azomethine ylide precursors including the methyl 3,4-dihydro-6,7-dimethoxyisoquinoline-3carboxylate moiety were synthesized. The 1,3-dipolar species formed from these products react with activated dipolarophilic olefines leading diastereospecifically to derivatives of 4′,5′-dimethoxy-1,2-benzo-4,7-imino-4-methoxycarbonyl-1-cycloheptene. Proton magnetic resonance data allowed the determination of the stereochemistry of the cycloadducts. Key words: cyclic azomethine ylide, azabicyclic compounds, stereochemistry.

Réaction du fluoroborate de 2-benzoyl-1,2-dihydro isoquinaldonitrile avec les esters α,β-éthyléniques. II. Cas des esters oléfiniques gem-disubstitués. Stéréochimie des produits de condensation–réarrangement, dérivés du 4,5-dihydro-3H-pyrrole

The previously suggested mechanism of the condensation–rearrangement reaction of a Reissert compound hydrofluoroborate salt with reactive olefins was reexamined in the case of methyl methacrylate, itaconate, citraconate, and mesaconate. Addition of triethylamine to the reaction medium leads to the isolation of a presumed intermediate 8. Spectrometric (proton magnetic resonance) data of the compounds 8 allow us to specify their stereochemistry and in two cases to point out an isomerization equilibrium. Keywords: Reissert compound fluoroborate salt, [4 + 2] cycloaddition, stereochemistry.

A nuclear magnetic resonance study of molecular motion in (2,4,5-Trichlorophenoxy)acetic acid

Proton magnetic resonance data in polycrystalline (2,4,5-trichlorophenoxy)acetic acid in the temperature range 77-400 K are reported in this communication. After a correction is made for the H-H distance in the methylene group the rigid lattice second moment (S2) coincides with the experimental value in the temperature range 77-170 K. The observed fall in S2 in the temperature range 170- 208 K is interpreted as the result of the CH2COOH group reorientation. The barrier height associated with the reorientation is found to be 8.728 kJ mol- which indicates non-cleavage of hydrogen-bonding in the dimeric unit during reorientation.

Proton NMR Studies of Amorphous Plasma-Deposited Films

ABSTRACTProton magnetic resonance data are presented for the hydrogen alloys of plasma-deposited amorphous boron, silicon, carbon, silicon carbide, and silicon nitride. Linewidth and lineshape analysis leads to the conclusion that hydrogen nuclei are clustered in a-Si/C:H, a-C:H, and a-Si/NiH. The a-Si/C:H and a-C:H data show that hydrogen exists in two phases. Modeling of linewidths in a-Si/C:H indicates that the two phases are heavily hydrogenated carbon clusters imbedded in a weakly hydrogenated silicon lattice. Evidence is also presented for the presence of motionally narrowed hydrogen spectra in a-B:H, a-Si/N:H and a-C:H. “B NMR spectra in a-B:H show no evidence of motional narrowing. It is suggested that the hydrogen nuclei giving rise to the motionally narrowed spectra are associated with disorder modes.

Proton magnetic resonance studies of 2′-deoxynucleosides and nucleotides in the syn conformation

Proton magnetic resonance data for 6-methyl-2′-deoxyuridine and its 3′- and 5′-monophosphate derivatives are obtained in aqueous solution and compared with data for corresponding thymine derivatives. The data show that the derivatives of the 6-methyluracil base occupy the syn conformation. The presence of the syn base leads to a flattening of the sugar ring and destabilization of the g+ conformer about the C(4′)—C(5′) bond. This destabilization is particularly large at the 5′-nucleotide level and is discussed in terms of a repulsive interaction involving the 2-keto oxygen of the base and the negatively charged 5′-group.

Polybrominated derivatives of 5α-androstane and 5α-estrane 3-ketones: cyclopropanol formation

Bromohydrin acetates from sodium borohydride reduction of di- and tribrominated 17β-hydroxy-5α-androstan-3-one and 17β-hydroxy-5α-estran-3-one have been prepared and their structures determined by spectroscopic methods. Some 220 MHz proton magnetic resonance data are reported for structure determination. The formation of cyclosteroid derivatives by 1,3-elimination of bromine with zinc–copper couple is discussed.