Carbon-13 chemical shifts of α,β-unsaturated acids

Carbon-13 spectra of 59 α,β-unsaturated carboxylic acids have been measured. Large differential shieldings of ethylenic carbons in the cis and trans isomers of acrylic acid derivatives were found (altogether 15 isomeric Z- and E-pairs of acids were investigated). The origin of differential shieldings is complex and both molecular ground states as well as changes in excited states appear to be involved. All measured ¹³C chemical shifts can be described by additive parameters that provide a straightforward new technique by which structural assignments can be made for a wide variety of isomeric mono-, di- and tri- substituted α,β-unsaturated acids.     

Synthesis of novel α,α′,β-trisubstituted β-lactones

A concise and efficient synthesis of α,α′,β-trisubstituted β-lactones is presented. These novel lactones are easily obtained in five steps and will be dedicated to anionic ring opening polymerization.     

Effect of tin tetrachloride on thermal decompositions of α,α′-azobisisobutyronitrile and dimethyl α,α′-azobisisobutyrate

Thermal decomposition of α,α′-azobisisobutyronitrile (AIBN) and dimethyl α,α′-azobisisobutyrate (MAIB) in the presence of a large amount of tin tetrachloride was investigated to determine the effect of complex formation on the decomposition rates and yields of the recombination products. The addition of tin tetrachloride significantly increased the decomposition rates; the observed first-order rate constant increased by factors of 4.5 and 17 at molar ratios of [SnCl₄]/[AIBN] = 21.65 and [SnCl₄]/[MAIB] = 19.53, respectively. It was found that the decomposition of these azo compounds was also accelerated by the addition of a comparable amount of donor solvent such as ethyl acetate or propionitrile to tin tetrachloride and that the enhancement in rate was accounted for by a larger frequency factor in the Arrhenius equation. Furthermore, the addition of tin tetrachloride seemed to suppress the formation of recombination products, tetramethyl succinonitrile and dimethyl tetramethylsuccinate, of the radicals produced by decomposition.     

A novel synthesis of α-hydroxy- and α,α′-dihydroxyketone from α-iodo and α,α′-diiodo ketone using photoirradiation

A novel reaction of α-iodo ketone (α-iodocycloalkanone, α-iodo-β-alkoxy ester, and α-iodoacyclicketone) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketone in good yields. In the case of α,α′-diiodo ketone, α,α′-dihydroxyketone which little has been reported until now was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′-dihydroxyketone.     

Photochemical Reactions. 126th Communication. Photochemistry of an α, β: δ, ε-unsaturated ketone: 4-(2′, 7′, 7′-Trimethylbicyclo [3.2.0]hept-2′-en-1′-yl)-3-buten-2-one

On ¹n,π*-excitation, the title compound 2 undergoes a photoinduced intramolecular [4 + 2]-cycloaddition affording the tetracyclic enol ether 3 as the only product in 79% yield. The assigned structure of 3 was confirmed by its conversion to the p-nitrobenzoate 6 whose structure was determined by X-ray analysis.     

Carbon Magnetic Resonance Spectra of α, β, γ, δ- and α, β, α′, β′- Unsaturated Ketones

Carbon-13 spectra of a series of 26 unsaturated ketones (ortho- and para-cyclo-hexadienones and corresponding open-chain analogues) have been measured by Fourier-transform. Pulse spectroscopy. A complete analysis has been achieved by means of double resonance experiments using noise-modulated and coherent off-resonance proton irradiation and with the aid of non-decoupled spectra. Chemical shifts are interpreted in terms of charge distribution in the dienone system and of methyl substituent effects. Carbon chemical shifts were also obtained for O-protonated ortho- and para-cyclohexadienones. One-bond and long-range carbon-proton and carbon-fluorine spin coupling constants are reported for several compounds.     

13C NMR of organosulfur compounds the 13C chemical shifts of monocyclic γ- and δ-sultones

The ¹³C NMR spectra of several monocyclic γ-sultones(1,2-oxathiolane 2,2-dioxides) and δ-sultones(1,2-oxathiane 2,2-dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C-α carbon, but do not appear to be important for C-α. Anisotropic deshielding also appears to be important for the chemical shifts of C-α, but the effects on C-α appear to be small. Dipole changes at C-α and C-α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C-α. Substituent effects are readily explained in terms of well-known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ-sultones proximate to the sulfonate group are found to be more deshielded than those of the γ-sultones.     

Electronegativity and linear electric field effect on γ-anti 13C chemical shifts

The contribution from the existence of a 1,3-diaxial H-α ?H-γ arrangement to the γ-anti effects of substituents X, which was previously believed to be generally shielding, is shown to be extremely dependent on the electronegativity of substituent X. In the presence of axial γ-substituents Y, linear electric field effects appear to play a significant role if the C-γ—Y bond is highly polarizable.     

Downfield γ-gauche and γ-antiperiplanar effects on 13C NMR chemical shifts exerted by thiophene sulphur

The γ-effects of sulphur on ¹³C NMR chemical shifts have been measured in a series of steroidal compounds containing the thiophene ring in different configurations with respect to the rest of the molecule. The data constitute the first example of downfield effects exerted by sulphur on both gauche and antiperiplanar γ-carbons. The γ-gauche effect of sulphur amounts to 1.6–1.8 ppm, the γ-antiperiplanar effect from practically zero to almost 1 ppm.     

Polyesters,polycarbonate, and polyurethanes from a novel monomer: α,α,α′,α′-tetramethyl-1,4-tetrafluorobenzenedimethanol

The novel diol monomer, α,α,α′,α′-tetramethyl-1,4-tetrafluorobenzenedimethanol, has been synthesized by a convenient route which involves the addition of acetone to 1,4-dilithiotetrafluorobenzene and can be purified by washing with hexanes. It does not directly undergo condensation polymerizations with diacid chlorides. Its disodium salt, prepared by its reaction with sodium hydride, similarly fails to undergo such polymerizations readily. However, the dilithium salt, prepared in situ by the reaction of the title diol with 2 equiv of n-butyllithium in tetrahydrofuran, is suitable for the preparation of various classes of condensation polymers. Four polyesters and one polycarbonate derived from the reactions of the dilithium salt of the diol with adipoly dichloride, sebacoyl dichloride, isophthaloyl dichloride, terephthaloyl dichloride, and phosgene and two polyurethanes derived from its reactions with tolylene-2,4-diisocyanate and methylene-di-1,4-phenyl diisocyanate were prepared. Each was fully characterized by GPC, NMR, IR, and UV-visible spectroscopies, and the results of these studies are reported herein. © 1993 John Wiley & Sons, Inc.     

Prediction of ortho(β) 13C chemical shifts in conjugated systems

An equation has been developed which relates ortho or C-β ¹³C substituent chemical shifts (SCS) to the ortho proton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho ¹H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho ¹³C data in 2-naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.     

Synthesis and stereochemistry of (3α)-6β,7β-dihydroxy- and 6β-hydroxy-8-alkyl-8-azabicyclo[3.2.1]octane-3-spiro-5′-imidazoline-2′,4′-diones

The synthesis of 6β-hydroxy- and 6β,7β-dihydroxy-8-alkyl-8-azabicyclo[3.2.1]octane-3-spiro-5′-hydantoins was stereoselectively achieved by Bucherer-Bergs reaction of the corresponding ketones. An α configuration on C₃ was proposed for all hydantoins on the basis of spectral data.     

8-Aza-7-deaza-2′,3′-dideoxyguanosine: Deoxygenation of its 2′deoxy-β-D-ribofuranoside

The synthesis of 6-amino-1-(2′,3′-dideoxy-β-D -glycero-pentofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( =8-aza-7-deaza-2′,3′-dideoxyguanosine; 1 ) from its 2′-deoxyribofuranoside 5a by a five-step deoxygenation route is described. The precursor of 5a, 3a , was prepared by solid-liquid phase-transfer glyscosylation which gave higher yields (57%) than the liquid-liquid method. Ammonoloysis of 3b furnished the diamino nucleoside 3c . Compound 1 was less acid sensitive at the N-glycosydic bond than 2′,3′-dideoxyguanosine ( 2 ).     

The first enzymatic resolution of quaternary α′-acetoxy α,β-unsaturated cyclohexenones and cyclopentenones

The enantioselective resolution of various quaternary α′-acetoxy α,β-unsaturated cyclohexenones and cyclopentenones was performed with the commercially available enzyme CCL in pH = 8.0 phosphate buffer. Various parameters that would affect the enantioselectivities were tested and the best enzymatic resolution conditions were found to afford the enantiomerically enriched quaternary acetoxylated substrates with high ee varying between 36% and 99%.