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.     

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 $\text{6}$).     

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 $\text{7}$.     

1,2-Homoheptafulvene: Synthesis and cycloaddition

1,2-Hemoheptafulvene ($\text{2}$) was synthesized and reacted with 4-phenyl-1,2,4-triazoline-3,5-dione to yield [4π + 2π] and [6π + 2σ + 2π] cycloadducts.     

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.     

Cycloaddition reactions of 2,3-didehydrothiophene generated by flow vacuum thermolysis of thiophene-2,3-dicarboxylic anhydride

Flow vacuum thermolysis (FVT) of thiophene-2,3-dicarboxylic anhydride ($\text{2}$) in the presence of 2,3-dimethylbutadiene ($\text{6}$) gives, in addition to 5,6-dimethylthianaphthene ($\text{9}$). small quantities of a dihydrodimethylthianaphthene ($\text{12}$) and another dimethylthianaphthene ($\text{13}$) which is probably also formed by dehydrogenation of $\text{12}$ with chloranil. The partial structures of these minor products are consistent with their being formed by a [2+2]-cycloaddition between $\text{6}$ and an intermediate aryne, 2,3-didehydrothiophene ($\text{1}$), followed by a rearrangement of the resulting adduct $\text{11}$ and dehydrogenation. FVT of $\text{2}$ in the presence of 2,5- ($\text{17b}$) or 3,4-dimethylthiophene ($\text{17c}$) also gave a mixture of the dimethylthianaphthenes ($\text{18}$$\text{22}$, $\text{23}$) which can be rationalized as arising by a [4+2]- and two [2+2]-cycloadditions of the aryne $\text{1}$ to the thiophenes $\text{17}$ with subsequent desulfurization. The lack of equilibration of the products $\text{18}$, $\text{22}$ and $\text{23}$, was demonstrated and their origin as a function of the structure and reactivity of the aryne $\text{1}$ discussed.     

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.     

Zur konformation und intramolekularen beweglichkeit von [6]paracyclophan-8,9-dicarbonsäurediethylester)

The title compound 1 prepers the conformations $\text{1a}$/$\text{1b}$ predicted for [6]paracyclophane; the barrier for the intramolecular process $\text{la}$ ? $\text{1b}$ was found to be Δ G⁺ = 13.9 kcal/mol at +4°C.     

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].     

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.     

Comparison of cationic rhodium and iridium complexes in directed homogeneous hydrogenation

The hydrogenation of $\text{endo}$-6-methylenebicyclo[2,2,2]octan-2-ol catalysed by a range of rhodium and iridium complexes has been investigated. Unlike the corresponding $\text{exo}$-alcohol, reduction is highly stereoselective leading to 95 – 99.7% of $\text{endo}$-exo-6-methylbicyclo[2,2,2]octan-2-ol. Selectivity is much less pronounced for the corresponding methyl ether. Rhodium catalysts promote a competitive isomerisation of the double bond to $\text{endo}$-6-methyl-bicyclo[2,2,2]oct-5-en-2-ol, of which an authentic sample was reduced in high yield to pure $\text{exo}$-$\text{endo}$ product. Reduction of both $\text{endo}$-hydroxy substrates by iridium complexes is rapid and highly selective.NMR studies employing europium shift reagents played a central part in defining the stereochemical interrelationships of 2,6-disubstituted bicyclo[2,2,2]octanes.     

Photooxygenation of bicyclopropylidene

Upon photooxidation bicyclopropylidene ($\text{1}$) yields spiro[2.3]hexan-4-one ($\text{4}$) and 7-oxatrispiro[2.0.2.1]heptane ($\text{6}$). The formation of these is rationalized. Authentic $\text{6}$ was prepared by epoxidation of $\text{1}$, and $\text{4}$ by isomerization of $\text{6}$.     

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.     

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 ($\text{25}$).     

Novel photoisomerization of 5-chloro-1,4-dihydro-9-methyl-naphthalen-1,4-imine

Direct photolysis of 5-chloro-1,4-dihydro-9-methyl-naphthalen-1,4-imine in cyclohexane gave a mixture of 1-chloronaphthalene and isomeric dihydrocyclobut[b]indoles $\text{5}$ and $\text{6}$. Dihydrocyclobut[b]indoles $\text{5}$ and $\text{6}$ thermally rearranged to give 1-benzazepines $\text{7}$ and $\text{8}$, respectively.     

Cationic polar cycloaddition with chloromethyl phenyl sulfides

Chloromethyl phenyl sulfides $\text{3}$ underwent [4⁺ +2] type polar cyclo-additions with styrene, trans-stilbene, and phenylacetylene in the presence of stannic chloride to afford the thiochroman $\text{4}$, $\text{5}$ and thiochromen derivatives $\text{6}$. Under the same reaction conditions, N-allyl-α-chloro-α-(phenylthio)acetamide ($\text{7}$) gave the intramolecular cycloaddition product $\text{8}$.     

A simple route to the 8-oxabicyclo[3.2.1]octyl and 9-oxabicyclo[3.3.1]nonyl systems. Synthesis of the 8-oxa analog of cocaine.

In the presence of titanium tetrachloride, 1,3-bis(trimethylsiloxy)-1-methoxybuta-1,3-diene condenses with hexane-2,5-dione or 2,5-dimethoxytetrahydrofuran to give the 8-oxabicyclo[3.2.1]octyl compounds $\text{3}$ and $\text{6}$ respectively, and with 2,6-dimethoxytetrahydropyran to give the 9-oxabicyclo [3.3.1]nonyl derivative $\text{8}$. Compound $\text{6}$ is converted to a compound ($\text{9}$) which is the 8-oxa analog of cocaine.     

BH3 THF reduction of 3-methylisoxazolo [4,5-c]pyridines

3-Methylisoxazolo[4,5-c]pyridine $\text{1}$ on reduction with BH₃:THF gave, via the isolable complex $\text{4}$, the tetrahydroisoxazolopyridine $\text{5}$. The presence of two chlorine atoms at the 4 and 6 positions directed borane attact to the isoxazole ring, yielding the aminoethylpyridine $\text{8}$. Both types of reduction were obtained with 6-chloroisoxazolo[4,5-c]pyridine $\text{7}$.     

Fluorescent nucleoside analogues : Synthesis of fluorescent pyrido[2,1-i]purines,and their corresponding ribosides

Fluorescent pyrido[2,1-i]purines can in principle be obtained via Michael-addition of a suitable anion of a purine derivative to an acetylenic ester, followed by based-catalyzed cyclization, as depicted in Scheme II. 6-Substituted purine-derivatives are obtained via nucleophilic substitution of 6-chloro- and 6-methylsulfonylpurine ($\text{8a}$ and $\text{8b}$). In the presence of methyl propiolate and sodium methoxide, before cyclization, two consecutive Michael-additions take place, leading to $\text{13}$ and $\text{14}$. With substituted acetylenic esters, cyclization occurs after one Michael-addition. Michael-additions with ethylenic esters did not lead to expected cyclization products, except in cases where oxidation took place. -For the conversion of the pyrido[2,1-i]purines into the corresponding ribosides protection against nucleophilic attack was necessary.     

On the properties of some substituted α'-lithiated α(z), -butadienyl sulfides: cyclisations and rearrangements

The conditions for the preparation and cyclisation of the title compounds $\text{3}$ are described. The stability of the intermediate lithio-thiacyclohexenes $\text{4}$ is shown to depend on the reaction conditions and the substituents R¹-R⁴. The final products $\text{6}$, $\text{10}$ and $\text{7}$ arise from $\text{4}$ via a [1.4] sigmatropic rearrangement, a [1.3]prototropic shift followed by a [2.3] sigmatropic rearrangement, or the elimination of lithium methanethiolate respectively.