[2+2] Cycloaddition of benzyne to cis,trans- and cis,cis-1,5-cyclooctadiene

The relative rates of formation of $\text{cis}$ and $\text{trans}$ [2+2]cycloadducts of benzyne to $\text{cis}$, $\text{trans}$- and $\text{cis}$, $\text{cis}$-1,5-cyclooctadiene, $\text{trans}$- and $\text{cis}$-cyclooctene are discussed and properties of the adducts (e.g., their unusual hydrogenation) are described.     

Intramolecular Diels-Alder reactions of ethyl 2,4,9-decatrienoate and 2,4,10-undecatrienoate

The title compounds undergo intramolecular Diels-Alder reactions at 180°C to give ester-substituted hydrindane and decalin ring systems, with $\text{trans}$/$\text{cis}$ ratios of 43:57 and 50:50, respectively.     

Elimination reactions of 1,2-dihalo-2,3,3-trifluorocyclobutanes

Elimination reactions on isomeric mixtures of $\text{cis}$ and $\text{trans}$ 1,2-dihalo-2,3,3-trifluorocyclobutanes are reported. In zinc-promoted dehalogenations a steady decrease in the relative amount of the $\text{trans}$ isomers compared to the $\text{cis}$ isomers occured, with 2,3,3-trifluorocyclobutene as the sole product. The $\text{cis}$ isomers reacted at a faster rate in potassium hydroxide induced eliminations to yield a slight predominance of 1-halo-2,3,3-trifluorocyclobutenes over 3-halo-3,4,4-trifluorocyclobutenes. However, with triethylamine as the inducing base, an increased rate of elimination from the $\text{trans}$ isomers was noted along with almost exclusive formation of 3-halo-3,4,4-trifluorocyclobutenes.     

Synthesis applications of aza-cope rearrangements. Stereoselective synthesis of trans-alkyl-cis-3a-aryloctahydroindolones.

The reaction of both $\text{cis}$- and $\text{trans}$-2-amino-1-(1-phenylvinyl)- cyclopentanols with aldehydes affords $\text{trans}$-2-alkyl-$\text{cis}$-3a-aryl-4-oxo-octahydro indoles stereoselectively.     

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).     

Formation of 1,2,4-dioxazolidines by electron-transfer photooxygenation of aziridines

DCA-sensitized photooxygenation of $\text{cis}$- and $\text{trans}$-2,3-diphenylaziridine in acetonitrile yields exclusively $\text{cis}$-3,5-diphenyl-1,2,4-dioxazolidine. Photooxygenation of N-alkyl- substituted 2,3-diphenylaziridines provides both isomers of the peroxide. The $\text{cis}$$\text{trans}$ ratio of isomers decreases with increasing size of the group on nitrogen. These stereochemical results provide support for a proposed mechanism involving addition of singlet oxygen to intermediate azomethine ylides.     

Conformational populations and rotational barriers in esters

The $\text{trans}$ conformations of methyl, ethyl and isopropyl formate were shown to be present in equilibrium in a polar solvent with the $\text{cis}$ conformations to significant (> 1% 230 K) but much lower extents than for t-butyl formate; rotational barriers for the former compounds are greaters.     

Synthesis of perfluorochemicals for use as blood substitutes,Part I. Electrochemical fluorination of N-methyldecahydroquinoline and N-methyldecahydroisoquinoline

Electrochemical fluorination of N-methyldecahydroquinoline afforded mainly a mixture of $\text{cis}$ and $\text{trans}$ N-(F-methyl)-F-decahydroquinoline, their rearranged isomers and F-propyl-F-cyclohexane arising from the cleavage at carbon-nitrogen bonds, in a ratio of approximately 2:4:6:3. N-Methyldecahydroisoquinoline was also fluorinated electrochemically to give a mixture of $\text{cis}$ and $\text{trans}$ N-(F-methyl)-F-decahydroisoquinoline, their rearranged isomers and 1-(F-ethyl)-2-(F-methyl)-F-cyclohexane in a ratio of approximately 4:4:6:1. No correlation was found between the $\text{cis}$ and $\text{trans}$ ratio of starting materials and that of the corresponding perfluorinated amines. Fluorination of N-methyl-1,2,3,4-tetrahydroquinoline gave much lower yields.     

Chemistry of singlet Oxygen. XXVII. Directing effect of methoxy group in additions to methoxystyrenes

A methoxy group on a styrene double bond directs O₂ attack $\text{cis}$, giving 1,4 addition if the phenyl is $\text{cis}$, or ene reaction if a CH₃ is $\text{cis}$. If no substituent is $\text{cis}$, 1,4 attack on the $\text{trans}$ phenyl occurs at a slower rate.     

12-S-CIS conformationally locked retinoids: Thermal and photochemical interconversions leading to new geometric isomers

For 12-$\text{s}$-$\text{cis}$ locked retinal analogues, thermal equilibria are established between 11-$\text{cis}$, 13-$\text{cis}$-1c and 13-$\text{cis}$-2c and between 9-$\text{cis}$, 11-$\text{cis}$, 13-$\text{cis}$-1d and 9-$\text{cis}$, 13-$\text{cis}$-2d; a photoisomerization occurs to transform 2c to $\text{all}$-$\text{trans}$-2a and 2d to 9-$\text{cis}$-2b     

Aminyl radical cyclization by means of anodic oxidation. Stereoselective synthesis of cis-1-methyl-2,5-disubstituted pyrrolidines

Neutral aminyl radicals generated by anodic oxidation of lithium alkenylamides 2 undergo a stereoselective cyclization to give $\text{cis}$-1-methyl-2,5-disubstituted pyrrolidines 4. Their $\text{cis}$ stereochemistry was confirmed by a comparison with $\text{trans}$-1,2-dimethyl-5-phenylpyrrolidine, the structure of which was established by X-ray crystallographic analysis of its quarternary ammonium bromide 6.     

Configurational isomer mixtures and c-protonation in some sterically crowded enaminones

Acylation of 1,3,3-trimethyl-2-methyleneindoline (Fischer's Base) gives enaminone derivatives which show unusual C-protonation and exist in solution as mixtures of the $\text{cis}$-s-$\text{cis}$ and $\text{cis}$-s-$\text{trans}$ configurations.     

Stereochemistry of the copper perchlorate or copper bromide-catalyzed decomposition of aryldiazomethanes to stilbenes

Several phenyldiazomethanes easily decompose to $\text{cis}$- and $\text{trans}$-stilbenes when treated with catalytic amounts of copper perchlorate or copper bromide at 20°C. The preferential formation of $\text{cis}$ isomer is particularly noteworthy. The stereochemistry and the mechanism of these reactions will be discussed.     

Stereochemistry of nucleophilic additions to hexafluoro-2-butyne

Base-catalysed additions of alcohols to F-2-butyne (1) give mainly products of $\text{trans}$-addition while $\text{cis}$-addition predominates in uncatalysed additions of alcohols carried out in a diluent. The stereochemistry of addition of diethylamine is very dependent on the solvent used and $\text{cis}$- or $\text{trans}$-addition may predominate. Stepwise and concerted mechanisms are advanced to account for these observations. Nucleophilic addition of sulphur to (1) gives F-tetramethylthiophene (68%) and hydration gives CF₃CH₂COCF₃ (91%).     

A study of periselectivity in the thermal cyclisation reactions of diene-conjugated diazo compounds: 1,7-cyclisation as a route to 3H-1,2-diazepines and 1,5-cyclisation leading to new rearrangement reactions of 3H-pyrazoles

A range of diene-conjugated diazo compounds has been generated by the thermal decomposition of the sodium salts of the tosylhydrazones of 1-acyl-1, 3-dienes. Those of type (21) with a $\text{cis}$ relationship of the diazo group and the γ, δ-double bond $\text{and}$ having a $\text{cis}$ hydrogen atom at the diene terminus cyclised only by 1,7 ring closure to give 3$\text{H}$-1,2-diazepines (23). This mode of cyclisation was inhibited by the presence of $\text{cis}$ methyl or phenyl groups at the diene terminus eg in (45). Compounds of this type cyclised by the alternative 1,5- ring closure to give 3-alkenyl-3$\text{H}$-pyrazoles eg (46) as primary products. These observations are explained on the basis of a helical transition state (54) for the 8π electron 1,7-electrocyclisation reaction. Diene-conjugated diazo compounds with a $\text{trans}$ γ,δ double bond eg (32) also cyclised predominantly by 1,5-electrocyclisation to give 3-alkenyl-3$\text{H}$-pyrazoles eg (33). In most cases the 3$\text{H}$-pyrazoles rearranged under the reaction conditions $\text{via}$ alkenyl group and hydrogen migrations to give 1$\text{H}$-pyrazoles eg (34) and (37).     

Intramolecular diels-alder reactions of dienamines with acrylates: trends in stereoselectivity upon substitution.

Intramolecular Diels-Alder reactions of all-$\text{trans}$ ethyl 10-diethylamino-2,7,9-decatrienoate and 11-diethylamino-2,8,10-trienoate occur readily to produce $\text{trans}$ and $\text{cis}$-fused products in ratios of 85:15 and 55:45, respectively.     

Direct determination of the configuration of a benzenediazotate: The crystal structure of sy2-sodium benzenediazotate-4-sulphonate

The crystal structure of $\text{syn}$-sodium benzenediazotate-4-sulphonate shows this to be the $\text{cis}$- and not the $\text{trans}$-isomer     

Orbital and Conformational Preferences in Rearrangements of 1-Phenyl-1-Propylidenes

The stereochemistry of rearrangement of substituted 1-phenyl-1-propylidene to $\text{trans}$ and $\text{cis}$-propenylbenzenes is substituent dependent.     

Alicyclische verbindungen-v. darstellung diverser 1,3-butadienylcyclobutane

$\text{cis}$-($\text{3}$) and $\text{trans}$-1,3-Butadienylcyclobutane ($\text{4}$), all-$\text{trans}$-1-(1 ,3-butadieny1 )-2- vinylcyclobutane ($\text{10}$), and all-$\text{trans}$-1,2-bis(1,3-butadienyl)cyclobutane ($\text{15}$) have been prepared from readily available starting materials, and pyrolyzed to various cyclohexenes.     

Synthesis of 2-alkylthio (or trifluoromethylthio)-2-halogenoethenyl derivatives by means of wittig (under phase transfer conditions) or wittig-horner reactions. Application in the field of pyrethroids

A mixture of RSCHCl₂, Ph₃P and $\text{trans}$-caronaldehyde ethyl ester, treated with aq.NaOH under phase transfer conditions, gave the corresponding 2-alkylthio,2-chloroethenyl derivative, the product of the Wittig reaction of a phosphorane formed 'in situ'. The analogous derivative of the $\text{cis}$- and the 2-methylthio, 2-bromoethenyl derivative of the $\text{trans}$-caronaldehyde ethyl ester were synthesized also by means of Wittig-Horner reactions. The 2-trifluoromethylthio, 2-chloro-ethenyl derivative of the caronaldehyde ethyl ester ($\text{cis}$-$\text{trans}$ mixture) was also obtained through the phosphonate prepared from CF₃Cl + N₂CHP(OET)₂→ CF₃SCHClP(O)(OEt) The new derivatives prepared were converted to final pyrethroids by esterification with cyano(m-phenoxyphenyl)methanol.