Intercyclic [π 2+σ2+σ2]-and π2+ π2]-cycloaddition reactions in sterically fixed norbornadiene-/quadricyclane-systems

The stereoelectronic prerequisites for unusual “zipper-type” [_π 2+_σ 2+_σ 2]- and [_π 2+_π 2]-reaction sequences, e.g. in the still unknown C₇H₆-pentamers (1)/(2), are being studied using model compounds with systematically varied geometrical parameters. In line with expectations based on model considerations, in the [3]-series ((6), (7)) $\text{intracyclic}$, in the [5]-series ((10), (11)) $\text{inter}$cyclic processes clearly predominate.     

Photochemistry of bichromophoric systems. Silicon guided intramolecular 9, 10 : 1′, 2′ anthracene photodimerization in bis(9-anthryl) dimethylsilane.

Irradiation of bis(9-anthryl)dimethylsilane ($\text{1}$) generates a single photocyclomer formed by (4π + 2π) intramolecular 9,10 : 1′,2′ anthracene photodimerization. The influence of the silicon atom was investigated by reaction quantum yield determination and fluorescence study (stationary state and lifetimes).     

The solution photochemistry of αβ-unsaturated sulphones

1-Phenyl-2-(benzenesulphonyl)-ethylene and 1-phenyl-2-(benzenesulphonyl)-prop-1-ene have been shown to undergo $\text{Z}$,$\text{E}$-photoisomerisation, whereas 2-benzenesulphonylindene readily forms [_π2 + _π2] photoadducts with 2,3-dimethylbut-2-ene, cyclopentene, and cyclohexene.     

Cycloaddition reactions of 2H-benzo[b]thiete and conjugated cyclic dienes

2H-Benzo[b]thiete 1 reacts with cyclopentadiene 3 in consecutive [8π + 2π]cycloadditions yielding the condensed heterocycles 6–8 . Tetracyclone 9 on the other hand gives only the monoadduct 10 . An [8π + 8π]cycloaddition can be observed for 1 and diphenylisobenzofuran 11 . The related π system 13 shows again consecutive [477π + 27π]processes ( 1 + 13 ← 14, 15 ).     

The octant rule. XIV. synthesis and circular dichroism of α-exo and endo-deuteriobicyclo[3.2.1]octan-3-one and 6,6-dimethybicyclo[3.1.1]heptan-3-one

(1R,5S)-2S-Deuteriobicyclo[3.2.1]octan-3-one ($\text{1}$) and (1R,5S)-2R-Deuteriobicyclo[3.2.1]octan-3-one ($\text{2}$), prepared by diazomethane ring enlargement of (1S,4R)-2(exo)-deuteriobicyclo-[2.2.1] heptan-2-one and (1S,4R)-2(endo)-deuteriobicyclo[2.2.1]heptan-2-one respectively, both gave (?) n-π^* circular dichroism (CD) Cotton effects, Δε^max₂₉₄ = ?0.05 and Δε^max₂₉₄=?0.1, respectively, in hydrocarbon solvent. (1S,5R)-2S-Deuterio-6,6-diaethylbicyclo[3.1.1] heptan-3-one ($\text{3}$) and (1S,5R)-2R-deuterio-6,6-dimethylbicyclo[3.1.1] heptan-3-one ($\text{4}$), prepared from (-) myrtenal, both exhibited extraordinary vibrational fine structure for the n-π^* CD transitions observed in hydrocarbon solvent and oppositely?signed CEs, Δε^max₂₈₂=?0.01 and Δε^max₂₇₉=+0.01 respectively in CF₃CH₂OH solvent.     

Photo-oxygenations of 1H-azepine derivatives isolation and characterization of the [6+2] cycloaddition product

The reactions of 1H-azepine derivatives ($\text{1a-b}$ and $\text{4}$) with singlet oxygen gave the [6+2] cycloadducts ($\text{2a-b}$) and the [4+2] cycloadducts ($\text{3a-b}$ and $\text{5}$). The thermal and base-catalyzed rearrangements of the oxygen-adducts were investigated.     

v-Triazolines. part XXI. Spiro[bicyclo[2.2.1]hept-2-ene[54']1',2'.s'-triazole]derivatives from cyclopentadiene and 5-amino-4-methylene-v-triazolines

1R^*, 4R^*, 5S^*, 5'S^*-5'-Amino-1'-(4-nitrophenyl)-4',5'-dihydrospiro[bicyclo [2.2. 1]hept-2-ene[5.4]-1',2',3'-triazoles]$\text{2}$ have been obtained both by ?4 +2]-cycloaddition of cyclopentadiene to amino-methylene-1-(4-nitrophenyl)-4,5-dihydro-v-triazoles $\text{1}$ and by [3+2]-cycloaddition of 4-nitrophenylazide to 5-aminomethylene-2-norborenes $\text{4}$. The configuration has been fully established by X-ray crystallographic analysis. The course of the cycloaddition and the thermal behaviour of $\text{2}$ are discussed.     

The octant rule. XVI1. COnformation and circular dichroism of syn and anti 2-methylbicyclo[3.1.0]hexan-3-ones,thujone and isothujone

(lS,5S)-exo-2(R)-Methylbicyclo[3.1.0]hexan-3-one ($\text{1}$) and (lS,5S)-endo-2(S)-methylbicyclo[3.1.0]hexan-3-one (2) were synthesized and their circular dichroism (CD) spectra run. Conformational analysis based on molecular mechanics calculations and Karplus equation analyses of vicinal H¦H NMR coupling constants indicate boat-like sofa conformations for both $\text{1}$ and $\text{2}$, with very little ring distortion from the symmetry of the parent bicyclo[3.1.0]hexan-3-one. The lone dissymmetric ψ-axial and ψ-equatorial methyl groups of $\text{1}$ and $\text{2}$, respectively, are both octant consignate. The natural product analogs of $\text{1}$ and $\text{2}$, (?)-3-isothujone ($\text{3}$) and (+)-3-thujone ($\text{4}$) were prepared and examined similarly. Their α-methyl perturbers dominate the CD n-π^★ Cotton effects.     

Photo-Induced diels-alder reaction. A novel route to trans fused benzobicyclo-[5.3.O]decanes and [5.4.O]undecanes

Photoisomerization of $\text{cis}$-benzocycloheptenone to $\text{trans}$ benzocycloheptenone and its [4 + 2] cycloaddition with selected dienes is reported for the synthesis of $\text{trans}$ fused benzobicyclo[5.3.0]decanes 10, 12 and benzobicyclo [5.4.0]undecanes 13, 15.     

Pyrrole studies—XXIV: The reactions of 1-methyl-2-vinylpyrrole and 1-phenyl-2-vinylpyrrole with dimethyl acetylenedicarboxylate

The reaction of dimethyl acetylenedicarboxylate with 1-methyl-2-vinylpyrrole is temperature dependent. At 80° the predominant reaction is the [4π + 2π] cycloaddition to give dimethyl 1-methyl-6,7-dihydroindole-4, 5-dicarboxylate, whereas at room temperature Michael addition of the acetylenic ester at the 5-position of the pyrrole ring to give fumaric and maleic ester derivatives also occurs. Unequivocal assignment of the configurations of the Michael adducts have been made on the basis of their ³J_CO,h coupling constants. 1-Phenyl-2-vinylpyrrole reacts with dimethyl acetylenedicarboxylate to give only the [4π + 2π] cycloadduct at room temperature and at elevated temperatures.     

[2π + 2π]-Cycloaddition of biadamantylidene to 4-phenyl-3<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazole-3,5(4<Emphasis Type="Italic">H</Emphasis>)-dione. Effects of temperature,high pressure,and solvent

The effects of temperature, solvent nature, and high hydrostatic pressure on the rate of the reaction of biadamantylidene with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione have been estimated. Significant shielding of the C=C double bond in biadamantylidene is responsible for the high entropy and volume of activation. Quantitative yield of the reaction in the temperature range 25?45°C is related to its exothermicity. The rate of the [2π + 2π]-cycloaddition unexpectedly weakly depends on the solvent polarity, which makes it radically different from the [2π + 2π]-reaction with tetracyanoethylene.     

Cycloadditions des arsoles a haute temperature

At room temperature 1-phenyl-2,5-dimethylarsole $\text{1}$ gives [4+2] cycloadditions with dienophiles whereas at 160 °C it yields arsenic atoms which react with tolane to give the 1,4-diarsabicyclo[2.2.2]octatriene $\text{8}$; 1,2,5-triphenylarsole $\text{2}$ is less reactive at room temperature but isomerizes at 160°C to give the 2$\text{H}$-arsole $\text{5}$ which reacts as a diene with tolane to yield the 1-arsanorbornadiene $\text{6}$, and as a dienophile through its AsC double bond with dimethylbutadiene to give the 1-arsabicyclo[4.3.0]nonadiene $\text{7}$.     

1,6- and 2,6-di-t-butyl-cyclopent [f] azulenide; double bond localization in a planar 14 π-perimeter

The stable diatropic 1,6- and 2,6-di-t-butyl-cyclo-pent[f]azulenides $\text{9a}$ and $\text{b}$ are prepared and shown to be dominated by polymethide conjugation rather than by 14π-perimeter conjugation.     

Synthesis of 1,2-acenaphtho-3,8-disubstituted-derivatives of cyclo-octatetraene

Acecyclone and related cyclopentadienones 11 react with dimethyl tricyclo[4.2.0.0^2,5]deca-3,7,9-triene-7, 8-dicarboxylate 1 in refluxing xylene to afford the cyclo-octatetraenes 12, via a sequence involving [4+2]π-cycloaddition, cheletropic loss of carbon monoxide, extrusion of dimethyl phthalate by [4+2]π-cycloreversion, and finally valence isomerisation by retro-6π electrocyclisation. NMR evidence indicates that the products 12 contain rigid, bond-fixed, non-planar cyclo-octatetraene rings.     

Complete enantiospecificity in the highly regioselective and stereoselective photo- and thermal rearrangements of some homoconjugated ketones

The oxa-di-π-methane (ODPM) photorearrangement of 2-(carbomethoxy)spiro [5.5]undeca-1,3-diene-7-one ($\text{1}$d) to $\text{2}$d and the latter's thermal rearrangement to $\text{3}$d were shown to be not only fully regio-and stereoselective but also to occur with complete enantiospecificity. An additional example, the 2-hydroxymethyl derivative ($\text{1}$f) was also studied and the two systems were chemically correlated.     

Reaction of bicyclo[3.2.1]octadiene with 4-methyl-1,2,4-triazoline-3,5-dione: competitive dipolar and homo-cycloaddition

The nonconjugated bicyclo[3.2.1]octa-2,6-diene ($\text{1}$) affords with 4-methyl-1,2,4-triazolin-3,5-dione (MTAD) the homo-cycloadduct ($\text{2}$) product and the rearranged urazoles ($\text{3}$) and ($\text{4}$) through dipolar cycloaddition, while ene-reaction and (2+2)-cycloaddition are not observed.     

cis-Oxa,aza-σ-homobenzenes : Syntheses,[2+2+2]-cycloreversion reactions

$\text{cis}$-Dioxa,aza-tris-(8) and $\text{cis}$-oxa, aza-bis-σ-homobenzenes (21) have been synthesised. With activation barriers, which clearly support the concerted mechanism, they undergo [2+2+2]-cycloreversion yielding 7H-1,4,7-dioxazonines (9) and 4H-1,4-oxazocines (22), resp.     

Addition and cycloaddition reactions of allenyl cations with various cycloalka-1,3-dienes

Allenyl cations

, generated $\text{in}$$\text{situ}$ from propargyl chlorides and zinc chloride give monocyclic adducts or [3+4] and [2+4] cycloaddition products with various cycloalka-1,3-dienes. The mode of addition depends on R and the ring size of the 1,3-dienes.     

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 ($\text{25}$).     

Erzeugung und cycloaddition von allyliumionen aus α-halogenketonen unter solvolyse-bedingungen

Some α-haloketones react with furan in methanolic solution in the presence of base to form the 3-oxo-8-oxabicyclo[3.2.1]oct-6-enes ($\text{11}$), the products derived from a [4+3] cycloaddition of an allylium intermediate ($\text{5}$ or $\text{6}$).