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.     

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     

[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.     

Structure and conformation of heterocycles. 13. conformational analysis of 2,3-DI(R)OXY-1,4-dioxanes: anomeric and gauche effects

A series of $\text{trans}$- and $\text{cis}$-2,3-di R)oxy-1,4-dIoxanes (R = Me,Ph, Ac) and some 2,5-disubstituted analogis were prepared and analysed by various NMR techniques. The $\text{trans}$ isomers occur in more than 96% as diaxial conformers. Molecular mechanics calculations largely confirm these findings, which are interpreted -in terms of combined anomeric and gauche effects.     

Synthesis and conformational properties of 5,7-disubstituted [3.3] Metacyclo (2,5) thiophenophane-1,12-diones

The title compounds showed unique conformational equilibria which were dependent upon the substituents in the 5,7-positions, the predominant conformers being in a $\text{syn}$ O,S,O-$\text{cis}$,$\text{cis}$ conformation with a highly deformed thiophene-2,5-dicarbonyl moiety.     

Stereospecific synthesis of cis-2-alkenylcyclopropane carboxylic acids; A total synthesis of (±)-cis-chrysanthemic acid

A stereospecific route to $\text{cis}$-2,2-dimethyl-3-alkenyl-cyclopropanecarboxylic Acids is illustrated by a total synthesis of (±)-$\text{cis}$-Chrysanthemic Acid (11). The key step consists of an alicyclic Claisen rearrangement of $\text{O}$-silyl enolates derived from appropriately substituted ($\text{Z}$)-4-hexen-6-olides [e.g.(9)].     

cis Δ5-octahydro-1-naphtalenones and cis Δ5-decahydro-1-naphthalenes (cis-1-decalones) by stereoselective intramolecular diels-alder reaction.

Intramolecular DIELS-ALDER reactions of requisite trienes led to $\text{cis}$-1-decalones, $\text{via}$ an endo intermediate state.     

Substituted cyclononatetraenes and nonafulvenes

Reaction of $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-[9]annulene anion ($\text{1}$) with electrophiles ($\text{2a}$-$\text{d}$) leads to substituted $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-1,3,5,7-cyclononatetraenes ($\text{3a}$-$\text{d}$) which are precursors for the preparation of 10- and 10,10′-donor-substituted nonafulvenes (e.g. $\text{7b′}$$\text{e′}$). The influence of solvent and temperature on the ¹H-nmr spectra of the nonafulvenes $\text{7b′}$-$\text{h′}$ has been investigated.     

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).     

Bis(tricarbonyliron) complexes of P-quinodimethanes: fragmentation and isomerisation under electron impact

EI mass spectra of $\text{trans}$-η⁴,η⁴-[3,6-bis(methylene)-1,4-cyclohexadiene]-bis=(tricarbonyliron) complexes $\text{1a}$, $\text{b}$ are reported. The fragmentation pathway is rationalized by assuming a rearrangement of the $\text{trans}$-bis(tricarbonyliron) complexes into the $\text{cis}$-isomers under electron impact.     

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     

Synthesis of 4-substituted cis,cis-1,6-cyclodecadienes via cycloalkylation

Cycloalkylation of dimethyl malonate and tosylmethylisocyanide with $\text{cis}$,$\text{cis}$-1,9-dibromonona-2,7-diene has demonstrated the feasibility of direct cyclization as a route to functionalized $\text{cis}$,$\text{cis}$-1,6-cyclodecadienes.     

The unexpected thermal instability of 3,4-tetramethylene-1,2-dioxetane as compared to that of cis-3,4-diethyl-1,2-dioxetane.

3,4-Tetramethylene- and $\text{cis}$-3,4-diethyl-1,2-dioxetane ($\text{1}$ and $\text{2}$) were prepared and characterized (for $\text{1}$ - Ea = 22.5 kcal/mole, log A = 12.8; for $\text{2}$ - Ea = 24.5 kcal/mole, log A = 13.1).     

Olefin metathesis in polycyclic frames 1. A new way to cis, syn, cis - tricyclopentanoids (acs-C11-triquinanes)

A novel olefin metathesis sequence permits ready access to functionalised $\text{cis}$, $\text{syn}$, $\text{cis}$-tricyclo [6.3.0.0^2,6] undecane based bis-enones. These bis-enones have been shown to undergo cage cyclisation in sunlight with remarkable ease and efficiency.     

β-tributylstannylacrylates. Stereospecific synthesis via conjugate additon of tributylstaknylcopper

The synthesis of $\text{cis}$- and $\text{trans}$-8-tributylstannylacrylates from conjugate addition of tributylstannylcopper to various β-substituted acrylates is shown to be a highly stereospecific reaction. Of four tributylstannylmetal reagents examined for this conversion, optimum results were obtained with tributylstannylcopper.     

The effect of alkene configuration on the partitioning between the carbenic reactions and the 1,7-electrocyclisation of α-)o-alkenylaryl)diazoalkanes

The 1,7-electroclyclisation of α-($\text{o}$-alkenylaryl)diazoalkenes to 1$\text{H}$-2,3-benzodiazepines is blocked by the $\text{cis}$ substituent in $\text{Z}$ alkenyl groups and the diazo-compounds then react via alternative routes including a new intramolecular carbene reaction to give naphtho[a]cycloheptenes.     

A highly effective asymmetric synthesis of α-hydroxy acids by alkylation of chiral n-(benzyloxyacetyl)-trans-2,5-bis(methoxymethoxymethyl)pyrrolidine

Alkylation of lithiated $\text{N}$-(benzyloxyacetyl)-$\text{trans}$-2,5-bis(mehtoxyymethoxymethyl)- pyrrolidine proceeded with high stereoselectivity (≥96% de) and subsequent transformations of the alkylated products gave synthetically useful α-benzyloxy acids or α-hydroxy acids of high enantiomeric purity.     

Asymmetric aldol reaction of amide enolates bearing trans-2,5-disubstituted pyrrolidines as chiral auxiliaries

Condensation of aldehydes with Zr enolate of chiral $\text{N}$-propionyl-$\text{trans}$-2,5-disubstituted pyrrolidine proceeded with high diastereo- and diastereoface-selection. Stereoselectivity in the reaction of the corresponding $\text{N}$-acetyl compounds was also examined.     

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.     

Rearrangement spinal en serie a/b cis : conversion du lithocholate de methyle en derives du d-homoandrostane

A new backbone rearrangement is observed in A/B $\text{cis}$ methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters $\text{1}$ by AgSbFg₆ or by the action of the triflic anhydride on the si1y1ated ether $\text{2}$. This rearrangement leads to methyl diacholenate $\text{3}$ and new lactones in D-homoandrostane series $\text{5}$ and $\text{6}$. The differences of behaviour between A/B $\text{cis}$ and A/B $\text{trans}$ series and the mechanism of rearrangements are discussed.