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.     

Electronic spectra of 12-S-CIS conformationally locked retinals

The electronic absorption spectra of the four new 12-$\text{s}$-$\text{cis}$-locked retinals (1a–1d) bearing 7-$\text{trans}$, 11-$\text{trans}$ double bond geometries are described and compared with those of analogous 7-$\text{trans}$, 11-$\text{cis}$-geometries (1e–1h) and parent retinals (2a-h).     

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 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.     

Acid-catalysed decomposition of (20 R) and (20 S)-20-azido-5α-pregnane : bis steroids Schiff base formation via imine coupling.

BF₃-OEt₂ decompostion of azides $\text{1}$ or $\text{2}$ leads to the coupling product Schiff base $\text{6}$$\text{via}$ imine intermediates.     

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.     

A convenient one-pot procedure for the selective reduction of ketones in the presence of aldehydes

The title process has been accomplished by a three-step sequence involving protection of aldehyde as the imine, $\text{in situ}$ reduction of ketone with lithium tri-$\text{tert}$-butoxyaluminohydride, and regeneration of aldehyde on hydrolytic work-up.     

The synthesis and photodimerization of 2h-2-benzazepine-1,3-diones

The photochemical dimerization of 2$\text{H}$-2-benzazepine-1,3-diones has been described. The structures of the major products are assigned as the head-to-tail, 5, and the head-to-head. 7, photodimers on the basis of the analysis of the coupling constants in the NMR spectra. In addition, the structures of the minor products and attempts to convert 5 to 7 are discussed.     

Catalytic bimetalic [Pd(0)/Ag(I) Heck-1,3-dipolar cycloaddition cascade reactions accessing spiro-oxindoles. Concomitant in situ generation of azomethine ylides and dipolarophile

Spiro-oxindoles, epi-Spirotryprostatin A and its analogues were prepared from a tactical combination of cascade catalytic bimetallic Pd (0)/Ag(I), intramolecular Heck and subsequent imine → azomethine ylide → 1,3-Dipolar cycloaddition reactions. The cascade features in situ generation of azomethine ylides and dipolarophiles and produces two new rings together with three stereocentres in good to excellent yields.     

Biosynthetic pathway of iridoid glucosides in Gardenia jasminoides f. grandiflora cell suspension cultures after iridodial cation formation

Administration of ²H- or ¹³C-labeled monoterpenes to $\text{Gardenia}$$\text{jasminoides}$ f. $\text{grandiflora}$ cell suspension cultures demonstrated that iridoid glucosides of the suspension cultures are biosynthesized, after iridodial cation formation from 10-oxocitral (3), via 8-epiiridodial (13), 8-epiiridotrial (14), boschnaloside (8-epiiridotrial glucoside) (12) and dehydroiridotrial glucoside (8). In addition, the coexistence of a route via iridodial cation (4), dehydroiridodial (6), dehydroiridotrial (15) and dehydroiridotrial glucoside (8) is conceivable.     

A synthetic approach to (+)-aldosterone and its relatives (2)- a stereoselective synthesis of (+)-trans-4,5-(4-methoxybenzo)- 1β , 7aβ - ( 2α-methoxymethyl- 5 -oxofuro) hydrindane

A stereoselectivity in an intramolecular cycloaddition of the olefinic $\text{o}$-quinodimethanes 13 and 23 generated $\text{in}$$\text{situ}$ from the thermolysis of optically active 4β-[2-(4-methoxybenzocyclobutenyl)ethyl] -5α-methoxymethyl-3-phenyl-thio-methylenefuran-2-ones 12 and 22, respectively, is studied and a stereoselective synthesis of (+)-$\text{trans}$-4,5-( 4-methoxybenzo) -1β,7aβ-(2α-methoxymethyl-5-oxofuro)hydrindane 1 is also described.     

Photolysis of t-butyl azide in N2 at 12 K,and matrix IR spectra of three isomeric C4H9N imines

Photolysis of $\text{t}$-butyl azide in N₂ matrices at 12 K gives the imine 3a; matrix IR spectra for imines 4a and 5a are also reported.     

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.     

The unexpected intramolecular C-arylation of 2-0-benzylated cyclic sugar derivatives: a useful 1,2-cis-C-glycosylation reaction

Upon treatment with tin(IV) chloride, perbenzylated glycofuranosyl acetates such as 3 or 6 undergo an unusual, intramolecular α-$\text{C}$-arylation resulting from the internal Friedel-Crafts alkylation of the 2-$\text{O}$-benzyl substituent.     

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.     

Optically active 2-p-tolylsulfinylacrylate a novel chiral dienophile which exhibits high reactivity and diastereoselectivity

The Diels-Alder reaction of a novel chiral dienophile, alkyl ($\text{S}$)-2-$\text{p}$-tolylsulfinylacrylates 1 with anthracene and cyclopentadiene showed high diastereoselectivity under the chelation controlled condition.     

A facile transformation of bicyclic keto esters to bisprotected (±)-8-epithienamycin via enol activation

A facile “one-pot” transformation of bicyclic keto ester (2) to bisprotected (±)-8-epithienamycin $\text{via}$ enol phosphate activation followed by the addition-elimination reaction of $\text{N}$-protected cysteamine derivative is described.     

Transfer to monomer in the polymerization of N-(3-dimethylaminophenyl) maleimide and N-(3-dimethylamino-6-methylphenyl) maleimide

The kinetics of the homopolymerizations of styrene, N-(3-dimethylaminophenyl) maleimide (I) and N-(3-dimethylamino-6-methylphenyl) maleimide (II) in benzene and dimethylformamide, and the molecular weights of the polymers were studied. N-(3-Dimethylaminophenyl) succinimide, regarded as a model for polymer I, did not affect the polymerization of styrene. The data indicate degradative transfer of polymer radicals to dimethylformamide and pronounced transfer to monomers I and II (C_M ≈ 0.06–0.07). The value of $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for II is 0.09 $\text{dm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$$\text{mole}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$$\text{s}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$.     

Revised structures of pratorinine and pratorimine

Two phenanthridone alkaloids isolated from the bulbs of $\text{Crinum bulbispermum}$ L. have been shown to be identical with pratorinine and pratorimine. The structure proposed earlier for pratorinine has been revised to 3 on the basis of an X-ray structure analysis and the structure of pratorimine has been shown to be 2.     

The first x-ray structure determination of a z-phosphaethylene: z-2-phenyl-1-(2,4,6-tri-t-butylphenyl)phosphaethylene

The sterically protected $\text{Z}$-phosphaethylene, $\text{Z}$-2-phenyl-1-(2,4,6-tri-t-butylphenyl)phosphaethylene (1-Z), was analyzed by X-ray crystallography.