Acid-catalysed reactions of 3,5-dialkyl-spiro[2.5]Octa-2,5-dien-4-ones

Acid-catalysed ring opening of the spirodienones ($\text{2a}$) and ($\text{2b}$) using p-toluene-sulphonic acid affords the styrène derivatives ($\text{3a}$) and ($\text{3b}$), while treatment with acetic anhydride/H₂SO₄ affords the furan derivatives ($\text{4a}$) and ($\text{4b}$).     

Synthesis of oxazolidin-2-ones using carbonate ion on a polymeric support

Through the insertion of a carbon dioxide molecule, the oxazolidin-2-ones ($\text{5a}$) and ($\text{5b}$) were prepared by treataent of the salts ($\text{4a}$) and ($\text{4b}$) with carbonate anion on polymeric support. The hydrolysis under basic conditions of ($\text{5a}$) and ($\text{5b}$) afforded the erythro-3-amino-1,2-diols ($\text{6a}$) and ($\text{6b}$) which were fully acetylated: the 2-amino-2-deoxyerythritol derivative ($\text{7b}$) was obtained in 91% yield.     

Kationische cyclisierung von (Z)-und (E)-1,3-dimethyl-2-(3-hexenyl)-2-cyclohexenol

The cationic cyclization of the carbinol $\text{3a}$(Z) occurred stereoselectively and resulted in a mixture of the hydrindane $\text{4a}$ and the octalin $\text{5a}$, both with $\text{trans-}$configuration of side chain and angular methyl group. Cyclization of $\text{3b}$(E) yielded in $\text{4b}$ and $\text{5b}$, both with $\text{cis}$-configuration. The structure of $\text{4a}$,$\text{5a}$ was proved by transformation to the diketones $\text{8}$,$\text{9}$.     

Amino substituted 1-oxa-3-azabutatrienium salts: preparation, structure and reaction with carbonyl compounds

N,N-Dimethylformamide ($\text{4a}$) and N,N-dimethylpivalamide ($\text{4b}$) react with carbonyl chloride isocyanate ($\text{5}$) in the presence of antimony pentachloride to afford the amino substituted 1-oxa-3-azabutatrienium hexachloroantimonates $\text{6a}$,$\text{b}$. An X-ray diffraction analysis of $\text{6a}$ confirms the proposed structure. The heterocumulenes $\text{6a}$,$\text{b}$ react with aldehydes, ketones and tertiary carboxamides to give the amino substituted 2-azaallenium salts $\text{13a}$-$\text{O}$ in high yields.     

Aromatisierung von cytclohexenon-derivaten über selenorganische zwischenstufen

Reaction of the hydroaromatic compounds ($\text{1a}$) and ($\text{3a}$) with lithium-diisopropylamide followed by phenylselenenyl chloride gives the selenides ($\text{1b}$) and ($\text{1c}$) resp. ($\text{3b}$), which form exclusively the phenols ($\text{4}$) resp. ($\text{6}$) after oxidation with 3-chloroperbenzoic acid in the presence of 3,5-dimethoxyaniline ($\text{7a}$).     

Stereoselektive synthese von α-glucosiden mit 1,1′ -diacetal-struktur

Reaction of ($\text{1b}$) and ($\text{1d}$) with the acetal ($\text{2a}$) in presence of trimethylsilyl trifluoromethanesulfonate at ?70° C gives the α-glucosides ($\text{3a}$) and ($\text{4a}$), whereas ($\text{1a}$) and ($\text{1c}$) lead to the β-glucosides ($\text{4c}$) and ($\text{4b}$). At 0° C reaction of ($\text{1a}$) with the acetals ($\text{2b-g}$) gives exclusively the α-glucosides ($\text{3b-g}$).     

Conjugative cycloaddition of N-chlorosulfonyl isocyanate across vinylcyclopropane system. A new pathway towards macro-heterocycles

trans- -Isopropenyl-4-methylene-spiro[2.x]alkanes ($\text{4a}$ and $\text{4b}$) react at 0°C with CSI to give as major products the trans bicyclic cycloazanondienones ($\text{12a}$-$\text{12b}$) and as the minor products bicyclodihydro-azepinones ($\text{11a}$ and $\text{11b}$), and the respective cis isomer of bicyclic cycloazanondienones ($\text{13a}$ and $\text{13b}$).     

Oxidative decarboxylation of [n.2.2]propellane carboxylic acids with lead tetraacetate. rearrangement approach to bicyclo [n.2.2.]bridgehead alkenes.

Oxidative decarboxylation of [n.2.2]propellane carboxylic acids ($\text{1a}$-$\text{c}$) with lead tetraacetate gave the bicyclic acetates ($\text{2b}$, $\text{c}$) having a bridgehead double bond and/or the tricyclic acetates ($\text{3a}$, $\text{b}$) in good yields. Vapor phase thermolysis of $\text{3a}$ or $\text{3b}$ afforded the bridgehead olefin $\text{2a}$ or $\text{2b}$ quantatively.     

The vinylketene acetal route to aklavinone and 11-deoxydaunomycinone

11-Deoxyanthracyclinone precursors $\text{6a}$ and $\text{6b}$ have been prepared regiospecifically by the reaction of bromojuglone methyl ethers $\text{4a}$ and $\text{4b}$ with vinylketene acetal $\text{5}$, prepared from the Hagemann's ester ketal $\text{7a}$.     

Synthesis and physical properties of 6,12-diarylazuleno[1,2-b]azulenes

The structure of a minor dimer ($\text{2a}$) of 1-arylcycloheptatrienylidenethylene was determined by X-ray crystallography. Dehydration of $\text{2a}$ and $\text{2b}$ gave novel non-benzenoid aromatics---6,12-diarylazuleno[1,2-b]azulenes ($\text{3a}$ and $\text{3b}$), whose electronic and NMR spectral properties were reported.     

Enamine chemistry-XXVI: The [4 + 2] cycloaddition reactions of 3-amino-1-(4-nitrophenyl)-prop-2-ene-1-thione with electrophilic olefins and acetylenes

Enamino-thiones 1 prepared from the corresponding enaminones by thiation with Lawesson's Reagent, were allowed to react with 2-chloroacrylonitrile and dimethyl acetylenedicarboxylate giving dihydro-2$\text{H}$-thiopyrans, 2, and 4$\text{H}$-thipyrans, 3, respectively. The reaction of 1a with ethyl propiolate at room temperature afforded 4$\text{H}$-thipyrans, 4a, which on standing rearranged to 2$\text{H}$-thiopyran, 5a(1, 3 amide shift). The reaction of 1b with ethyl propiolate produced 4b and 5b. Some of the ¹³C NMR data are reported.     

A nitrosamine route to (±)-macrostomine

In a synthetic approach to macrostomine $\text{1}$, both side chains of the isoquinoline nucleus are attached by high yield carbon carbon bond formation with lithiated nitrosamines ($\text{2b}$ → $\text{3a}$, $\text{3c}$ → $\text{4a}$).     

Synthesis of enantiomerically enriched atrolactic acid and other α-hydroxy acids

The α-anions of 2-substituted 1,3-dioxolan-4-ones derived from chiral mandelic and lactic acid ($\text{2a}$, $\text{2b}$; $\text{3a}$; $\text{10a}$, $\text{10b}$) were alkylated with high stereoselectivity. The products formed were hydrolysed to α-hydroxy acids with 65–85% e.e. ((S)(+)-$\text{5}$,$\text{7}$,$\text{9}$, (R)(–)-$\text{13}$).     

Formal total synthesis of β-pipitzol

(±)-$\text{O}$-methylperezone ($\text{1b}$) was obtained by selective oxidative demethylation of (±)-leucoperezone trimethyl ether ($\text{4a}$). Compound ($\text{4a}$) was prepared by condensation of 2,3,5-trimethoxytoluene ($\text{5e}$) with 6-methyl-5-hepten-2-one, followed by reductive removal of the tertiary alcohol. The aromatic precursor $\text{5e}$ was prepared in four steps from 2,3-dimethoxytoluene ($\text{5a}$) and, alternatively, in three steps from 5-bromoveratraldehyde ($\text{6a}$). Racemic $\text{1b}$ and $\text{4a}$ were directly compared with the optically active molecules prepared from natural R(-)-perezone ($\text{1a}$).     

Zur deprotonierung von chloromethyleniminiumchloriden

Deprotonation of chloromethyleniminium chlorides ($\text{1}$, $\text{13}$) leads to cis-trans-isomeres 1,2-diamino-1,2-dichloro-ethenes ($\text{3a}$, $\text{3b}$ resp. $\text{14a}$, $\text{14b}$); their reactivity is described.     

A convergent synthesis of substituted pyrrolidines by 1,3 dipolar cycloaddition

Thiazolium ylids $\text{2a}$ and $\text{2b}$ are converted to $\text{4}$ in 3 steps.     

Base catalyzed rearrangement of some bicyclic ketol acetates.

The ketol $\text{3a}$ and its acetate $\text{3b}$ when refluxed in methanolic potassium hydroxide (5%) were found to rearrange to 4-methyl-8-acetyl-5,6,7,8-tetrahydro-1-naphthol $\text{4}$. The epimeric acetate $\text{3c}$ also behaved likewise. A mechanism is suggested for the rearrangement.     

Regioselektive synthese von catenarin und erythroglaucin

A new synthesis of the naturally occurring anthraquinones catenarin ($\text{8a}$) and erythroglaucin ($\text{8b}$) involves regioselective addition of $\text{4b}$ to the anhydride $\text{2b}$.     

Intramolecular azide cycloaddition to a photochemically generated zwitterion

Photochemical rearrangements of 2,5-cyclohexadienones $\text{7a}$ and $\text{7b}$ to bridged triazenes $\text{11a}$ and $\text{11b}$$\text{via}$ zwitterions $\text{10a}$ and $\text{10b}$ are described.