Acid catalyzed isomerization of bicyclic alkenes: a facile betweenanene synthesis

Isomerization of $\text{cis}$-bicyclo[10.8.0]eicos-1(12)-ene ($\text{1a}$) and $\text{cis}$-bicyclo[10.10.0]docos-1(12)-ene ($\text{1b}$) to [10.8]- and [10.10]betweenanene ($\text{2a}$ and $\text{2b}$) has been effected by sulfuric acid. In both cases, the betweenanene isomers were found to predominate at equilibrium (70/30 $\text{2a}$/$\text{1a}$ and 95/5> $\text{2b}$/$\text{1b}$).     

A facile synthesis of strained bridgehead olefins by a gas-phase elimination reaction

A synthesis of bicyclo[3.3.1]non-1-ene $\text{1}$ and of a 10:1 mixture of bicyclo[4.2.1]non-1(8)-ene $\text{2}$ and bicyclo[4.2.1]non-1(2)-ene $\text{3}$ by gas-phase pyrolysis of the corresponding bridgehead acetates and chlorides is reported.     

Palladium-catalyzed cyclization reactions : Unique synthesis of condensed thiazoles

The facile synthesis of 3-methylene-2,3-dihydro-5H-thiazolo-[3,2-c]pyrimidin-5-ones ($\text{9}$) has been performed by the catalytic action of a Pd(II) salt on 4-propargylthiopyrimidin-2(1H)-ones ($\text{6}$).Similar Pd(II)-catalyzed cyclization of 3-propargylthio-1,2,4-triazin-5(2H)-ones ($\text{10}$) gives 6-methylene-6,7-dihydro-4H-thiazolo[2,3-c](1,2,4]-triazin-4-ones ($\text{11}$) as a main product. 3-Methylene-2,3-dihydro-7H-thiazolo[3,2-b][1,2,4]triazin-7-ones ($\text{12}$), the regioisomers of $\text{11}$ are provided by a base-catalyzed cyclization of [ulbar 10].     

A novel route to meta-aminobenzotrifluoride

Product patterns can be altered in reactions of $\text{m}$-nitrobenzotrichloride [VI] with [AHF]_x·NH₄F complex. Side-chain fluorination predominates under ‘mild’ conditions. In contrast. ‘forcing’ conditions affected unexpected $\text{in}$-$\text{situ}$ fluorination-reduction to give $\text{m}$-aminobenzotrifluoride [V] in high yield [75%] and purity [99.6%]. $\text{in}$-$\text{situ}$ reduction is probably initiated by a combination of iron from the stainless steel autoclave and trace amounts of moisture. The transformation of [VI] to [V] represents another type of $\text{in}$-$\text{situ}$ fluorination-reduction nitroaromatics, e.g. nitrobenzene [VII] to $\text{p}$-fluoroaniline [VIII]. $\text{o}$-Nitrobenzotrichloride [XI] degraded under ‘forcing’ conditions with [AHF]_x·NH₄F.     

Condensed cyclic and bridged-ring systems : part 12: A novel synthetic route to 4-p-methoxyphenyl-bicyclo[ 2.2.2 ]octan-2-ones and some bicyclo [ 3.2.1 ] octane derivatives by acid-catalyzed intramolecula

The efficacy of a new acid-catalyzed intramolecular C-alkylation has been demonstrated by the synthesis of 1-methyl-4-$\text{p}$-methoxyphenylbicyclo [2.2.2] octan-2-one ($\text{5}$) and 4-$\text{p}$-methoxyphenylbicyclo [2.2.2] octan-2-one ($\text{6}$) from easily accessible starting materials. The carbinol $\text{20}$, derived from $\text{5}$, undergoes facile rearrangement leading to 1-$\text{p}$-methoxyphenyl-4-methyl bicyclo [3.2.1] oct-3-ene ($\text{22}$), which has been transformed to $\text{endo}$-1-$\text{p}$-methoxyphenyl-4-methylbicyclo [3.2.1] octan-3-one ($\text{25}$).     

Reaction of neorl with thallium(III) perchlorate

Reaction of nerol ($\text{1}$) with thallium(III) perchlorate gave 6-oxabicyclo[3.2.1]octane derivatives ($\text{2}$) and ($\text{3}$), and 6,9-dioxabicyclo[3.3.1]nonane derivatives ($\text{4a–d}$) as the cyclization products.     

Bridgehead nitrogen heterocycles from 2,4,6-triphenyl- pyrylium cation and thiosemicarbazide or thiocarbohydrazide

2,4,6-Triphenylpyrylium with thiosemicarbazide and thiocarbohydrazide, gives 2-pyrazolines $\text{3a}$ and $\text{3b}$ which undergo cyclization yielding pyrazolo(1,5-c]pyrimidine 5 and pyrazolo [2,3-d]-1,2,4-triazepine $\text{7}$ derivatives, respectively. Reaction of $\text{7}$ with phenacyl bromides gave 1,3-thiazolo[3,2-b]pyrazolo [2,3-d]-1,2,4-triazepin-4-iums $\text{10}$. Compound $\text{3a}$ on treatment with phenacyl bromides gave 1-(4'-aryl-thiazol-2'-yl)-2-pyrazoline derivatives $\text{6}$. Compound $\text{3b}$ reacts with acyl chlorides to give pyrazolo[1,5-c]pyrimidine derivatives $\text{14}$, and with aromatic aldehydes giving the 2-(Δ^2'1 pyrazolin-1-yl)-5-aryl-1,3,4-Δ²-thiadiazolines $\text{12}$ which were easily converted to the corresponding 2-(Δ²-pyrazolin-1-yl)-5-aryl-1,3,4-thiadiazoles $\text{13}$.     

Palladium-catalyzed cyclization reactions of 3-propargylthio 1,2,4-triazin-5(2h)-ones to thiazolo-1,2,4-triazinones

Selective transformation of 3-propargylthio-1,2,4-triazin-5(2H)-ones ($\text{1}$) to 6-methylene-6,7-dihydro-4H-thiazolo[2,3-c][1,2,4]-triazin-4-ones ($\text{2}$) and 3-methylene-2,3-dihydro-7H-thiazolo[3,2-b]-[1,2,4]triazin-7-ones ($\text{3}$) is performed under the conditions of Pd(II) salt or sodium hydroxide catalysis, respectively.     

An improved synthesis of [2.2.3]cyclazines from 3H-pyrrolizines

[2.2.3]Cyclazines are obtained in moderate yields by reaction of 3$\text{H}$-pyrrolizines bearing conjugative substituents (Ph or CO₂Me) with vinamidinium salts in the presence of strong bases. Syntheses of the previously unknown 2-phenyl-3$\text{H}$-pyrrolizine and 1-methoxycarbonylcyclopenta [$\text{h}$] [2.2.4] cyclazine are also described.     

Photocyclization of benzofurancarboxanilides. Photorearrangement of the benzodihydrofuran system to 3-o-hydroxyphenylquinolones

$\text{cis}$-Dihydrobenzofuro[2,3-c]quinolone ($\text{4a}$) and $\text{cis}$-dihydrobenzofuro-[3,2-c]quinolone ($\text{5}$) undergo photorearrangement, characteristic to the benzodihydrofuran system, leading to 3-$\text{o}$-hydroxyphenylquinolone ($\text{6}$). A plausible mechanism involving a cyclopropyl dienone ($\text{12}$) was discussed.     

Synthesis of (1s,5r)-karahana ether and (1s,5r)-karahana lactone,the optically active forms of unique monoterpenes wit

(1$\text{S}$,5$\text{R}$)-(-)-Karahana ether (8,8-dimethyl-2-methylene-6-oxabi-cyclo[ 3.2.1]octane) and (1$\text{S}$,5$\text{R}$)-(-)-karahana lactone (8,8-dimethyl-2-methylene-6-oxabicyclo [3.2.1]octan-7-one) were synthesized from ($\text{S}$)-3-hydroxy-2,2-dimethylcyclo-hexanone. The natural karahana lactone was shown to be almost racemic ($\text{ca}$. 1.3 % e.e.).     

Valence isomerization of C9H10hydrocarbons: Photochemical reactions of bicyclo [3.2.2] nona-2,6,8-triene and its dihydro-derivatives

The valence isomerization reaction of bicyclo[3.2.2]nona-2,6,8-triene ($\text{2}$), which photoisomerized to two homologues of semibullvalene, was discussed with the photoreactions of its dihydro-dreivatives, bicyclo[3.2.2]nona-6,8-diene ($\text{3}$) and bicyclo[3.2.2]nona-2,6-diene ($\text{4}$).     

Synthesis and structure of stilbene crowns.

Syntheses of $\text{E}$- and $\text{Z}$-[a,e]-dibenzo-7,10,13-trioxacyclotrideca-1,3,5-triene, $\text{1}$ (n=1) and $\text{E}$- and $\text{Z}$-[e,a]-dibenzo-7,10,13,16-tetraoxacyclohexadeca-1,3,5-triene, $\text{1}$ (n=2) are described and the X-ray structure of E-$\text{1}$ (n=1) is reported.     

[1.1.1.1.1]paracyclophane and [1.1.1.1.1.1]paracyclophane

The first syntheses of [1.1.1.1.1]paracyclophane ($\text{1}$) and [1.1.1.1.1.1]paracyclophane ($\text{2}$) are described, featuring a trifluoroacetic acid promoted Friedel-Crafts cycloalkylation as the final step.     

The structures of the two isomers of monodehydro[14]annulene

Variable temperature ¹H nmr spectrometry has shown that the “unstable” isomer of monodehydro[14]annulene possesses the symmetrical di-$\text{trans}$ configuration $\text{1}$ or $\text{2}$, and the “stable” isomer (the precursor of [14]annulene) possesses the tri-$\text{trans}$ configuration $\text{4}$.     

The [4.4.4.4]Fenestranes and[2.2.2.2]paddlane. Prospects for the realization of planar tetracoordinate carbon?

Semi-empirical (MINDO/3 and UNDO) MO calculations on highly strained planar tetracoordinate carbon candidates indicate the central carbons in $\text{cis}$- [4.4.4.4] fenestrane ($\text{1}$) to have pyramidal ($\text{1a}$) and in trans-[4.4.4.]fenestrane ($\text{2}$) to have distorted tetrahedral ($\text{2a}$) geometries. In [2.2.2.2]paddlane ($\text{3}$), the two central carbons are pentacoordinate. Each is nearly coplanar with four carbon neighbours; additionally, the two bridgehead carbons are connected by a single bond ($\text{3a}$).     

Studies on the formation of [5]metacyclophane

Base induced elimination of HCl from the dichloro[5.3.1]propellane $\text{3a}$ gives a mixture of [5]metacyclophane ($\text{1}$) and tetrahydrocyclopentacyclooctenes ($\text{2}$), while the stereoisomeric $\text{3b}$ affords $\text{1}$ quantitatively.     

Reaction of 2-functionalized pyrylium salts with amidrazones

A number of derivatives of the bicyclic 1,2,4-triazolo [1,5-a] pyridine ($\text{3}$) and pyrido [2,1-f][1,2,4] triazine ($\text{4}$ and $\text{7}$) have been prepared by reaction of 2-methylthio- and 2-ethoricarbonyl-4, 6-diphenylpyrylium salts, respectively, with amidrazones.     

Acid catalyzed isomerization of large ring bicyclic alkenes: a reevaluation of some betweenanene synthetic strategy

Acid treatment of $\text{cis}$-bicyclo[10.10.0]docos-1(12)-ene (Ib) affords bicyclo[10.10.0]docos-1-ene ($\text{11}$) as the sole product. Contrary to a previous report, [10.10]betwwenanene (IIb) is not produced under acidic conditions. Attempts to convert cycloalkylidenecycloalkanes and spiro systems to fused ring alkenes by acid treatment were also unsuccessful.     

Sterically crowded cyclohexanes-2 synthesis,structure and dynamics of hexaspiro[2.0.3.0.2.0.3.0.2.0.3.0]heneicosane

The synthesis, structure and dynamics of hexaspiro[2.0.3.0.2.0.3.0.- 2.0.3.0]heneicosane $\text{3}$ are described. $\text{3}$ adopts a chair conformation in the crystal state but prefers a chair-to-twistboat equilibrium in solution. The activation parameters of the chair-to-chair interconversion of $\text{3}$ and the closely related hexaspiro[2.0.2.0.2.0.2.0.2.0.2.0]- octadecane ([6]rotane) $\text{4}$ have been determined by DNMR. Some consequences appertaining to the conformation and dynamics of other fully (cyclo-)alkylated cyclohexanes are discussed.