The chemistry of an azomethine imine derived from 2,3-dimethylindole and n-phenyl triazolinedione. A new and facile condensation method

The urazole 3 derived from 2,3-dimethylindole and PTAD has been found to be converted readily to the unusually stable azomethine imine 5 with $\text{t}$-butylhypochlorite followed by elimination of HCl. This azomethine imine has been shown to serve as a carbonyl-equivalent in a number of aldol-type condensations under mild conditions.     

The structure of tatsinine,a novel c19-diterpenoid alkaloid from delphinium tatsienense franch

A novel C₁₉-diterpenoid alkaloid designated as tatsinine has been isolated from the roots of $\text{Delphinium}$$\text{tataienence}$ and its structure (3) has been derived from ¹H NMR and ¹³C NMR spectroscopic evidence.     

o-quinone methides 2. Stereoselectivity in cycloaddition reactions of o-quinone methides with vinyl ethers

Cycloaddition reactions between vinyl ethers 3 and $\text{o}$-quinone methides 2, thermally generated from 2-hydroxybenzyl alcohols 1, have been studied. The structure and conformational preferences of the 4-substituted 2-ethoxy-(2,3)-dihydro-2$\text{H}$-benzopyrans 4–9 obtained, which show new interesting features, are discussed together with competitive kinetic data. The cycloaddition process is concerted and involves $\text{o}$-quinone methides in the $\text{E}$-configuration. The OEt-$\text{endo}$ transition state seems to be preferred with ethyl vinyl ether and $\text{Z}$-1-propenyl ethyl ether, whereas with $\text{E}$-1-propenyl ethyl ether the stereoselectivity of the cycloaddition process depends on substituents on the methylene group of the starting alcohol 1. These results are discussed in terms of $\text{endo}$ and $\text{exo}$ preference of the propenyl ether methyl group.     

Verbrückte und unverbrückte norbornyl-kationen in der gasphase. Berechnungen zur stabilität isomerer norbornyl-kationen mit hilfe quantenmechanischer verfahren

The geometry and the relative stability of bicyclic compounds 1–20 have been calculated by standard quantum mechanics methods.MINDO/3 yields the following stability order of isomeric norbornyl cations (relative energies in $\text{kcal}\text{mole}$): 1-norbornyl cation 9 (0.0); 1.7 σ-bridged cation 6 (0.7); 7-norbornyl cation (nonplanar) 7 (1.1); 2-norbornyl cation (classical) 2 (4.2); 7-norbornyl cation (planar) 8 (4.3); 2-norbornyl cation (bridged) 1 (6.1). The stability of the same ions calculated by ab initio methods (STO-3G, MINDO/3-geometry) leads to an order more nearly consistent with experimental results: 2-norbornyl cation (classical) 2 (0.0); 2-norbornyl cation (bridged) 1 (5.9); 7-norbornyl cation (planar) 8 (11.1); 1-norbornyl cation 9 (14.6); 7-norbornyl cation (nonplanar) 7 (21.2). For the secondary 7-norbornyl cation, MINDO/3 gives a pyramidal configuration, 3.2 $\text{kcal}\text{mole}$ more stable than the planar form. In contrast, the ab initio results (complete optimization of all geometrical parameters) indicate the planar cation to be the most stable form. The bridged structure of 2-norbornyl cation 1 is calculated (STO-3G, partly optimized) to be 4.3 $\text{kcal}\text{mole}$ less stable than the classical counterpart, 2. For the lower homologues 12 and 13 (STO-3G, complete geometry optimization), this difference is 6.4 $\text{kcal}\text{mole}$. However, more extended basis sets should favour the bridged structures. The hydrogen bridged norbornyl cations 3, 4, and 5 have been calculated (STO-3G, partly optimized) to be 14.4, 23.6 and 29.9 $\text{kcal}\text{mole}$ less stable than 2. The stability differences between the corresponding tertiary bicyclic ions 10 vs 11, and 14 vs 15 are calculated (ab initio) to be 15.3 and 19.0 kcal/mole, respectively, in favour of classical structures. The influence of methyl substitution at positions C₁ and C₆ (exo) on bridged and unbridged structure of 2-norbornyl cation is calculated. Pyramidal secondary and tertiary 2-norbornyl cations 19 (a; R=H, b; R=CH₃) and 20 (a; R=H, b; r=CH₃) have been used to model the electrical effects in the solvolysis transition states of epimeric 2-norbornyl esters. Due to more efficient hyperconjugation the pyramidal exo cation is stabilized more than the endo cation by 5.2 $\text{kcal}\text{mole}$ for the secondary series and 3.5 $\text{kcal}\text{mole}$ for the tertiary series. Bonding of endo cation 20 with a nucleophile should be stronger than bonding of exo cation 19 due to more efficient HOMO-LUMO interaction.     

Cyclotrimerization of cyclic diynes via metal atom cocondensation; revised structure for the reported “percyclophane-4”

A compound previously assigned the “percyclophane-4” structure $\text{3}$ has been shown to be the triyne $\text{2}$.     

Substituent influence on the indolization with pcl3 of some o,m,p-substituted phenylhydrazones

The indolization of deoxybenzoin $\text{o}$,$\text{m}$,$\text{p}$ (Me, MeO, Cl), $\text{p}$-NO₂ and $\text{m}$-EtO-phenylhydrazones (1) by the above reaction has been examined. All the reactions are carried out at room temperature and high yields of the corresponding indoles (2) are obtained even when -NO₂ substituent is present. In this case longer reaction time is necessary. Alkoxyphenylhydrazones give the corresponding indoles (2) in high yields without showing collateral reactions which indeed are present in several Fischer routes on these derivatives. $\text{m}$-Substituted phenylhydrazones (1) give a mixture of 4- and 6-substituted indoles in which the 6-isomer is always prevalent, a feature not inherent in the Fischer reactions. The regioselectivity is enhanced by the substituent steric hindrance increasing. The reaction can be also carried out at 0°C with a further improvement of its regioselectivity.     

Synthesis of novel macrobicyclic polyfunctional cryptands

A pathway yielding both $\text{syn}$ and $\text{anti}$-functionalized macrocycles derived from bis-tartaro-18-crown-6 (1) as well as a selective route to $\text{syn}$ compounds have been developed and applied to the synthesis of new macrobicyclic polyether cryptands (2) and (3), which may also be obtained by direct bridging of the dianhydride (4).     

Spirophosphoranes a liaison P-OH. Synthese,tautomerie

Spirophosphoranes with a P-OH bond have been prepared as free acid (compound 5c), triethylammonium salts (compounds 2c–6c), or adducts $\text{1}\text{1}$ with DMF (compounds 5c and 6c). The ionic feature of triethylammonium salts of compounds 1c–6c, shows that these Spirophosphoranes are relatively strong Brønsted's acids. Tautomeric equilibrium phosphoric ester—phosphorane with a P-OH bond [Scheme 9), shown in many cases, has been studied by means of ³¹PN, MRspectroscopy. Influence of factors ruling this equilibrium is analysed. Some elements of dynamic stereochemistry are examined.     

Untersuchungen an stoffwechselprodukten von mikroorganismen,-XXII1: Untersuchung der pigmente aus flavobacterium spec. stamm C12

The pigment complex from Flavobacterium spec strain C$\text{1}\text{2}$ consists of pigments 1a to 1d whose isolation and structure elucidations are reported. These pigments exclusively belong to the new class of flexirubin type pigments. Up to now, pigments of this type have been found in gliding bacteria only.     

Participation d'un groupe amide a la formation de sels de dioxolanne-1,3 ylium-2; Modele biomimetique de reaction de peptidation

An amide group is shown to be capable of intramolecular participation in the formation of an 1,3-dioxolan 2-ylium cation giving a tricyclic organic cation of a new type $\text{5a}$,$\text{b}$. This cation may be considered as a model of an electrophilic intermediate which might be formed from a peptidyl t-RNA during protein biosynthesis.The tricyclic salt $\text{5a}$,$\text{b}$ reacts with water and methanol like a classical dioxolenium salt. An amide acetal $\text{18}$ can be obtained from dimethylamine and 5a; hydrolysis of $\text{18}$ does not lead to the corresponding amide $\text{20}$ but to the cleavage of the CN. bond.     

Conformation and barrier to inversion of a 12-membered heterocycle containing two disulfide bonds

Raman and ¹H NMR spectroscopic data obtained for a dimeric product 4c formed on iodine oxidation of N-pnenyl-N-thiomethyl-thioglycolic acid amide (3c) indicate that this product is 4,11-diphenyl-4,11-diaza-1,2,7,8-tetrathia-cyclododecane-5,10-dione. The barrier to interconversion between the conformers of 4c has been determined by DNMR. The height of the barrier (ΔG^≠ = 17.3 ±0.1 $\text{kcal}\text{mol}$) is in agreement with the proposed structure. This investigation thus gives a support to the previously proposed mechanism of regiospecific dimeric oxidations of unsymmetrical dithols of type 3c.     

Structure elucidation and synthesis of (2s)-4-oxo-1-azabicyclo[3.3.0]octa-5,7-diehe-2-carboxylic acid,a new metabolite isolated ercm stheptomyces oliyacbjs

The structure of a new metabolite isolated from $\text{Streptomyces}$$\text{olivaceus}$ has been shown to be (2S)-4-oxo-1-azabicyclo[3.3.0]octa-5,7-diene-2-carboxylic acid by means of its spectroscopic properties and total synthesis.     

A method for the stereospecific synthesis of chiral cis-2-alkylcyclopropyllithium reagents

A general synthetic route to optically active $\text{cis}$-1,2-disubstituted cyclopropanes has been developed from the key intermediates 3 and 4.     

The stereochemistry of asteriscunolides: An x-ray based correction

The application of X-ray diffraction methods has shown that the configurations of Asteriscunolides A and B at the Δ⁹ double bond are Z, rather than those previously proposed E, while the stereochemistries of Asteriscunolides C and D were correctly established. Some unexpected NMR data and the new assignment of the spectral signals, based on 2D-NMR $\text{C}\text{H}$ correlations and NOE-difference experiments are reported.     

Isolation and structure determination of nigellicine,a novel alkaloid from the seeds of nigellasativa

The structure of nigellicine (1) , an unusual alkaloid from the seeds of $\text{Nigella}$$\text{sativa}$, was determined by x-ray diffraction and spectroscopic techniques.     

Acyclic stereoselection. 35. Effect of cation on diastereofacial selectivity in aldol reactions of a chiral α-silyloxy ketone.

By an appropriate choice of cation, three of the four possible aldols from the reactions of the chiral α-silyloxy ketone 1 with aldehydes may be obtained. The $\text{Z}$, lithium enolate provides 6, the $\text{Z}$, boron enolate gives 7, and the $\text{E}$ magnesium enolate affords 8.     

Structure of laurycolactone A and B,new C18 - quassinoids from Eurycoma longifolia and revised structured of Eurycomalactone (X - ray analysis)

Laurycolactone A $\text{2}$ and B $\text{3}$ are new quassinoids with a C₁₈ basic skeleton isolated from the Vietnamese Simaroubaceae, Eurycoma longifolia Jack. The structure of Eurycomalactone, a C₁₉ quassinoid isolated previously from the same plant, has been revised and shown to be $\text{4}$. The structures have been established by spectral means and those of $\text{2}$ and $\text{4}$ confirmed by X-ray diffraction analysis.     

On papaver bracteatum—XIV: Ready access to benzylidene phthalimidine compounds from rhoeadine alkaloid-derived nitriles

The $\text{B}\text{D}$trans lactole alpinigenine (1a) isolated from Papaver bracteatum Lindl. was shown to form the oxime 2a which in turn was transformed to the nitrile 3a by dehydration, the methiodide 4a, and — by treatment with alkali under mild conditions — to the benzylidene phthalimidine derivative 5a, whose structure was elucidated by spectral analysis as well as oxidative fragmentation into 6 and 7.The unique reaction leading to 5a apparently is bound with certain structural prerequisites inherent to 3a, including stereochemistry. When cis-alpinigenine (1b) was subjected to the same sequence, little of 5a accordingly could be obtained, and even none of any phthalimidine was formed from the non-acetoxylated nitrile 11.     

Nucleosides-126: Selective methylation of the C-nucleoside, ψ-isocytidine and its 2$́-deoxy analog. Synthesis of 1-methyl, 3-methyl and 4-o-methyl derivatives

Methods were developed to prepare 1 -methyl-, 3-methyl- and 4-0-methyl-ψ-isocytidine by selective methylation.3$\text{,}\text{?}$5$\text{-}\text{?}$O-Tetraisopropyldisiloxanyl-ψ isocytidine (8) was trimethylsilylated and then treated with MeI and, after deprotection, 1 -methyl-ψ isocytidine (6) was obtained. The 2$\text{-}\text{?}$deoxy analog (7) was also prepared in a similar manner from the 2$\text{-}\text{?}$deoxy analog (10) of 8. Treatment of 8 with CH₂N₂ afforded the 3-methyl-ψ-isocytidine derivative (19) as the major product. Methylation with diazomethane also occurred mainly on N3 of the 2$\text{-}\text{?}$deoxy analog 10 to form 20. Removal of the 3$\text{,}\text{?}$ 5$\text{-}\text{?}$O-protecting group from 19 and 20 afforded 3-methyl-ψ-isocytidine (14) and its 2-deoxy analog (15), respectively. 2-N-Acetyl- 3$\text{,}\text{?}$5$\text{-}\text{?}$O-tetraisopropyldisiloxanyl-ψ-isocytidine (24), on the other hand, gave the 4-O-methyl derivative (25) as the major product upon CH₂N₂ treatment. Subsequent deprotection of 25 afforded 4-O-methyl-ψ-isocytidine (29). aiv51b1p33b