Methyl substituent probe of the transition state for thermal decarbonylation of endo-tricyclo[3.2.1.02,4]octan-8-one

Methyl substituent probes at the C-2 and C-2,C-4 positions of $\text{endo}$-tricyclo[3.2.1.0^2,4] octan-8-one($\text{1}$) have provided kinetic evidence confirming the simultaneity of C-2,C-4 cyclopropane bond cleavage in the rate-determining step for thermal extrusion of carbon monoxide.     

13C-NMR studies of polyfluorinated hydrocarbons,carboxylic acid derivatives,alcohols and ethers

δ¹³C values and coupling constants (¹J(¹³C¹H), ¹J(¹³C¹³C), ⁿJ(¹⁹F¹³C) are reported for 19 polyfluorinated organic compounds. It is shown that the shielding of carbon depends upon the number of fluorine atoms in α -position. If the R_F-group is linked to a π -system hyperconjugative $\text{and}$ η-π interaction accounts for the δ¹³C data. The values ¹J(¹³C¹H) and ¹J(¹³C¹³C) are in qualitative agreement with changes of the s-character of the respective bonds.     

Delocalisation,conformation and basicity of anilines

¹³ C spectra of some anilines $\text{1}$ and annelated anilines $\text{2}$ are reported. Variations in the chemical shift of the para carbon atom are used to estimate twist angles of the amino group. Results so obtained are compared to base strength. It is found that in twisted anilines a rough correlation between twist angle and base strength exists.     

Novel rearrangement of twisted 2,4-di-alkyl 2-trans-4-trans pentadienals: An approach to cyclopentenones based on molecular mechanical consideration

Rearrangement of 2,4-di-$\text{trans}$-pentadienals $\text{IVa-d}$ was described as a consequence of the successive alkyl substitutions on the C-2 and C-4 positions. ¹H-FT nmr spectroscopy suggested that the reaction involves ketene $\text{VIII}$ as an intermediate.     

Synthesis of 13C and 15N labelled (S)-Tryptophan

(R,S)-serine-1-¹³C was incubated in a culture of $\text{Escherichia}$$\text{coli}$ cells to produce (S)-trytophan-1-¹³C. Bromoacetyl bromide-2-¹³C was converted to bromoacetanilide and cyclization of the anilide, followed by reduction and dehydrogenation furnished indole-3-¹³C. Indole-¹⁵N was synthesized by known sequences. These ¹³C and ¹⁵N isotomers of indole were converted by commercially available, lyophilized $\text{E}$. $\text{coli}$ to furnish (S)-tryptophan-γ-¹³C and (S)-tryptophan-indole-¹⁵N, respectively.     

Nucleophilic reactions of fluoroolefins. II. Regioselectivity and elimination-addition competition in the reaction of 1-phenylpentafluoropropenes with sodium ethoxide

1-Phenylpentafluoropropene and its para-substituted analogs $\text{1}$ are susceptible to nucleophilic attack at both vinylic carbon atoms C-1 and C-2. They react with ethanolio sodium ethoxide to give predominantly substitution products, 1-ethoxy-1-phenyltetrafluoropropenes $\text{2}$ and 2-ethoxy-1-phenyltetrafluoropropenes $\text{3}$, with only little formation of adducts, $\text{viz}$. 2-ethoxy-1H-1-phenylpentafluoropropanes $\text{4}$. Alkenes $\text{1}$, where the para-substituent X  H,Cl,and CF₃ give additionally 1,2-diethoxy-1-phenyltrifluoropropenes $\text{5}$ and, where X = CF₃ also 2,2-diethoxy-1H-1-phenyltetrafluoropropane $\text{6}$. Overall regioselectivity of nucleophilic attack of the ethoxide ion on alkenes $\text{1}$ exhibits the Hammett type correlation with Ó_p values of substituents X: CH₃O and CH₃ groups favour the attack on the vinylic carbon C-1, while CF₃ and Cl substituents direct the attack on the C-2 carbon of alkenes $\text{1}$. The E and Z isomers of 1-ethoxy and 1,2-diethoxy substituted alkenes $\text{2}$ and $\text{5}$ were formed in comparable amounts, while the E isomers of 2-ethoxy substituted alkenes $\text{3}$ were always formed with a 93 – 97 % selectivity.     

Biosynthesis of highly modified meroterpenoids in aspergillus variecolor. Incorporation of 13C-labelled acetates and methionine into anditomin and andilesin C

Incorporations of [1-¹³C]?, [2-¹³C]?, [1,2-¹³C₂]-acetates and [¹³C]-methionine into anditomin, a metabolite of $\text{Aspergillus variecolor}$, indicate its formation by a mixed polyketide-terpenoid biosynthetic pathway similar to that elucidated for andibenin; observations are made on the possible biosynthetic relationship of the $\text{A. variecolor}$ metabolites with austin and terretonin, mycotoxins recently isolated from $\text{A. ustus}$ and $\text{A. terreus}$ respectively.     

Biosynthesis of pebrolide

In pebrolide biosynthesised from MVA-[2.2-³H₂], 1, 1$\text{1}\text{3}$ and 2 tritium atoms respectively are retained at C-1, C-15 and C-7.     

Isolation and structural elucidation of heliangolidin,a new sesquiterpene lactone from artemisia canariensis

A new heliangolide has been isolated from aerial parts of $\text{Artemisia canariensis}$, and identified as (6$\text{E}$,10$\text{Z}$)(3$\text{S}$,3a$\text{R}$,4$\text{S}$,lla$\text{R}$)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3$\text{H}$, 4$\text{H}$) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, ¹H and ¹³C NMR, and two dimensional ¹H-¹³C chemical shift correlations) and X-ray diffraction analysis.     

Perfluoro-n-propylbromine(V) tetrafluoride

Perfluoro-$\text{n}$-propylbromine(V) tetrafluoride has been prepared by fluorination of perfluoro-$\text{n}$-propyl bromide at 0°C with elemental fluorine. It has been characterized by ¹⁹FNMR, mass spectroscopy and elemental analysis.     

From penicillin to penem and carbapenem. VI1) : Synthesis of dethiathienamycin

A new C₃-unit substitution reaction at C-4 position of 4- acetoxyazetidinone derivative ($\text{1}$ and $\text{5}$) by tetraallyltin ($\text{2}$) in the presence of 1/10 eq. of BF₃-ether in methylene chloride is described. From 4-allylazetidinone derivative ($\text{3}$) via ylid intermediate ($\text{14}$) dethiathienamycin ($\text{16}$) was synthesized.     

The structure of tamariscol,a new pacifigorgiane sesquiterpenoid alcohol from the liverwort frullania tamarisci

Tamariscol, a new sesquiterpenoid alcohol with the rare pacifigorgiane carbon skeleton, is a major constituent of the liverwort $\text{Frullania tamarisci}$, collected in Scotland. It has been assigned the structure and relative configuration (1) on the basis of ¹³C (including 2D INADEQUATE) and ¹H nmr spectroscopic evidence.     

Stereochemical studies 83 saturated heterocycles 76 : Preparation and conformational study of partially saturated 3,1-benzoxazines, 3,1-benzoxazin-2-ones and 3,1-benzoxazine-2-thiones

The $\text{cis}$- and $\text{trans}$-2-amino-4-cyclohexene-1-carboxylic acids $\text{1}$ and $\text{3}$ react with imidates to give the condensed-skeleton, bicyclic $\text{cis}$- and $\text{trans}$-pyrimidin-4-ones $\text{8}$ and $\text{9}$. The amino acids $\text{1}$ and $\text{3}$ were reduced to the $\text{cis}$-and $\text{trans}$-1, 3-aminoalcohoIs $\text{6}$ and $\text{7}$, which were cyclized by means of imidates to the bicyclic tetrahydro-4$\text{H}$-3,1-benzoxazines $\text{10}$ and $\text{11}$, or were converted, $\text{via}$ the corresponding carbamates $\text{14}$ and $\text{15}$ into the tetrahydro-4$\text{H}$-3,1-benzoxazin-2(1$\text{H}$)-ones $\text{16}$ and $\text{17}$. The 2-thioxo analogues $\text{18}$ and $\text{19}$ were prepared by cyclization of the dithiocarbamates obtained from the aminoalcohols $\text{6}$ and $\text{7}$ by treatment with carbon disulphide. The $\text{trans}$-aminoalcohol $\text{7}$ and its saturated analogue reacted with $\text{p}$-chlorobenzaldehyde to furnish the hexahydro $\text{13}$ and octahydro-4$\text{H}$-3,1-benzoxazine $\text{13a}$, respectively. ¹H and ¹³C NMR studies showed that, similarly to the earlier-investigated analogues containing oxygen or unsubstituted nitrogen at position 1, the synthesized $\text{cis}$ isomrs $\text{8}$, $\text{10}$, $\text{16}$ and $\text{18}$ occurred as the preferred conformer in the heterocyclic twist inverse form of $\text{N}$-inside type ($\text{quasiaxial}$ C₆-N bond) (B). In the $\text{trans}$ isomers containing a saturated C-2 atom ($\text{13}$ and $\text{13a}$), H-2 and H-6 are in $\text{cis}$ relative positions.     

Thermal equilibrium between “isoxazolidine” and “enamine”

Nitrones formed from the reaction of $\text{N}$-phenylhydroxylamine and aldehydes dimerized to isoxazolidines. A new thermal equilibrium between isoxazolidine and $\text{N}$-hydroxyenamine in DMSO was studied by ¹H and ¹³C NMR.     

Synthesis of Δ1-carbapenem derivative by aldol condensation method

The Δ¹-carbapenem derivative($\text{6}$) was prepared by the aldol condensation of the dialdehydic compound($\text{5}$) with piperidinium acetate. Careful hydride reduction followed by benzoylation gave $\text{7}$b, which was successfully decarbalkoxylated to $\text{8}$. The X-ray structure analysis of $\text{8}$ showed the C-3 carboxylate group and C-5 H are $\text{cis}$ each other.     

Strukturbestimmung von O-Methylazafrinmethylester durch 13C-NMR.-Spektroskopie

Structure Determination of Azafrin Methyl Ester 5-O-Monomethyl Ether by ¹³C-NMR.-Specta. The structure of the monomethyl ether ( 2 ) of azafrin methyl ester ( 1 ) was determined by a partial analysis of the ¹³C-NMR.-spectra. Assignments of quaternary carbon atoms and methyl groups in the cyclohexane ring were achieved using vicinal ¹³C-, ¹H-spin coupling. Substituent effects on methyl and methylene carbon atoms in 2 are discussed with respect to the conformation of the methoxy group. The spectra prove C(5)? OH as the site of methylation. Therefore C(5)? OH is less hindered than C(6)? OH.     

Stereochemical and compositional assignment of acrylonitrile/methyl methacrylate copolymers by DEPT and inverse HECTOR NMR spectroscopy

The acrylonitrile/methyl methacrylate copolymers of different monomer concentration were prepared by photo polymerization using uranyl ion as initiator. The carbon 13 and proton spectra of these copolymers are overlapping and complex. The complete spectral assignment of the ¹³C- and ¹H-NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and two dimensional ¹³C–¹H Heteronuclear Single Quantum Correlation (HSQC) experiments. The methylene, methine and the methyl carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used to ascertain the various geminal couplings between the methylene protons. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1081–1092, 1998     

Chiroptical studies of sugars. Part IV. Proposal of the glycosidic heteroatom [helicity rule in 1-thio-D-glycopyranosides

1-Thio-$\text{D}$-dlycopyranosides gave CD bands at 220 nm (n→δ^* of glycosidic sulfur). Their [θ] were shown as the sum of the two effects from ring oxygen and -OH at C-2, leading to the glycosidic heteroatom helicity rule to predict the configurations and conformations at C-1 and C-2.     

Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

We have measured the three hyperfine components of the spin—orbit split (²P_{$\text{3}\text{2}$} → ²P_{$\text{1}\text{2}$}) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm^?1), with the third line at 404.210 cm^?1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.