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 $\text{7a}$.     

Diborane as a reducing agent - VI the novel reduction of indole-1-carboxaldehydes to 1-methyl- indoles,di(indolyimethyl) ethers and indolylmethyl indolines

Reduction of the indole-1-carboxaldehydes ($\text{1a}$-$\text{1f}$) with borane /THF gives the 1-methylindoles ($\text{4}$) in 42-91-% yields together with the di(indolylmethyl)ethers ($\text{8}$), the indolyl-methyl indolines ($\text{7}$), the unsymmetric ether($\text{10}$) and the indolenine ($\text{11}$) as the minor products, except $\text{7a}$. This appears to be the first report on the formation of symmetric ethers in the borane/THF reduction of an oxygen function. The formation of $\text{7a}$ and $\text{7b}$ from $\text{1a}$ and $\text{1b}$ implies that electrophilic substitution takes place primarily at position 3 of 3-substituted indoles, $\text{1c - 1f}$ did not form the corresponding $\text{7}$ probably because of steric hindrance. These results are discussed in relation to the mechanisms of borane/THF reduction, origin of the different products and electrophilic substitution in 3-substituted indoles.     

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 $\text{13b}$).     

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)(–)-$\text{13}$).     

Korbförmige wirtmoleküle: : Tetrahydrofuran-Einschluss und Gast-selektive Katalyse des H/D-Austauschs in saurer Lösung

Macropolycyclic molecules ($\text{6a}$,$\text{b}$, $\text{7}$ and $\text{11}$) with an extended basket-shaped skeleton including a benzene ring, which acts as a floor plate, have been synthesized for the first time. The cavity of the hydrochloride of $\text{7}$ retains tetrahydrofuran even in water solution. The host $\text{6a}$ strongly accelerates guest-selective H/D exchanges in aromatic 1,3-diols.     

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.     

New synthesis of benzo [a]quinolizidin-2-ones via protected 2-aryl-4-piperidones

A new synthesis of 9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-benzo aquinolizin-2-one ($\text{1a}$ and its 3-ethyl derivative $\text{1b}$ via the corresponding 2-(3,4-dimethoxyphenyl)-4-piperidone ethylene acetals $\text{7}$ is reported. Alkylation of 2-arylpipendires $\text{7}$ with 2-bromoethanol followed by oxidation of the resulting amino alcohols $\text{9}$ with oxalyl chloride and dimethyl sulfoxide afforded the aldehydes $\text{10}$, which were cyclized with hydrochloric acid to give 7-hydroxybenzo[α]quinolizidines $\text{11}$. The reduction of $\text{1}$ with trinethylsilane and subsequent acid hydrolysis led to benzo aquinolizidin-2-ones $\text{1}$.     

A new synthesis of spirobenzylisoquinolines. Analogues of sibiricine and corydaine

The reduction product of dehydrocordrastine, $\text{6}$, with di-isobutylaluminum hydride spontaneously rearranged to the spirobenzylisoquinolines $\text{7a}$ and $\text{7b}$, analogous to the alkaloids sibiricine ($\text{5a}$), corydaine ($\text{5b}$), and yenhusomidine ($\text{5c}$).     

Fluorinated chromenes 1: 2,2,2-trifluoroethoxy precocene analogs and their corresponding 3,4-epoxides

Preparation of potential insect antijuvenile hormone agents 2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2H-chromene ($\text{3a}$), 6-methoxy-2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2$\text{H}$-chromene ($\text{3b}$) and 7-methoxy-2,2-dimethyl-6--(2,2,2-trifluoroethoxy)-2$\text{H}$-chromene ($\text{3c}$) and the corresponding 3,4-epoxides $\text{5a}$ and $\text{5b}$ is reported.     

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 ($\text{7a}$).     

The regiochemistry of intramolecular n-alkenylnitrone additions: preparative and mechanistic implications

The opposite regiochemistry, observed for the reactions $\text{7a}$ → $\text{8a}$ and $\text{7d}$ → $\text{8d}$, as compared with additions $\text{7b}$ → $\text{9b}$, $\text{7c}$ → $\text{9c}$ and $\text{7e}$ → $\text{9e}$, supports the hypothesis that in the transition state of nitrone-olefin additions the new C,C bond is more advanced than the C,0, bond. Further examples show the superimposition of substituent effects on this intramolecular control.     

Regiospecific synthesis of 11-desoxyanthracycline antibiotics starting with aloe-emodin

The regiospecific synthesis of an established 11-desoxyanthracycline synthon ($\text{8b}$) from aloe-emodin ($\text{3a}$) is described.     

Stereocontrolled synthesis of 7-hydroxy- and 7-acetoxy-PGI2: New stable PGI2 analogues

Stable analogues of PGI₂, 7-hydroxy- and 7-acetoxy-PGI₂, were synthesized from protected PGI₂ methyl ester $\text{1b}$via sulfoxides $\text{6a}$, $\text{6b}$ through stereocontrolled sulfoxide-sulfenate rearrangement.     

2-cyano Δ3 piperidines vi1 : a general method for the stereoselective synthesis of cis and trans 2,6-dialkylpiperidine alkaloids

The cis 2,6-dialkylpiperidine alkaloid (±) dihydro-pinidine $\text{7b}$ and the trans alkaloid (±) solenopsin A $\text{5a}$ were synthesized from a common α-aminonitrile synthon $\text{1}$. The key step in this synthesis was the stereoselective reductive decyanation of the 1-benzyl-2cyano-2′, 6-dialkylpiperidines $\text{3a}$ and $\text{3b}$.     

Unusual fragmentations under polonovski reaction conditions

N_b-oxides $\text{2a}$ and $\text{2b}$ in the presence of acetic anhydride led to products $\text{5}$, $\text{7}$ or $\text{8}$ with participation of the indole nucleus during the fragmentation reaction.     

Cycloaddition reactions of 1,3-benzothiazines - 6. Reactions of 1,3-benzothiazine derivatives with substituted acetyl chlorides

6, 7-Dimethoxy-2$\text{H}$-l,3-benzothiazine derivatives ($\text{1}$, $\text{8}$) react with substituted acetyl chlorides to give angularly condensed β -lactams ($\text{3a}$-$\text{d}$, $\text{10}$, $\text{11}$). The $\text{cis}$ compound $\text{11}$ was epimerised to the $\text{trans}$ derivative $\text{12}$. From the interaction of 2-phenyl-6,7-dimethoxy-4$\text{H}$-1,3-benzothiazine ($\text{7}$) and α -chloro-phenylacetyl chloride two stereoisomeric β -lactam derivatives ($\text{9a}$, $\text{b}$) were isolated, whereas in the other cases studied the reactions leading to β -lactams proved to be stereospecific. Analogous reactions of $\text{4}$-methyl-6,7-dimethoxy-2$\text{H}$-l,3-benzothiazine ($\text{5}$) furnished the enamides $\text{6a}$,$\text{c}$, $\text{d}$. Structures of the new compounds and configurations of the diastereomers were elucidated by IR and NMR spectroscopy.     

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.     

[2+2]-Cycloadditionen von vinylkationen

The vinylbromides $\text{1a}$ and $\text{1b}$ are allowed to react ith AgBF₄ and AgPF₆ in the presence of various olefins in CH₂Cl₂ as the solvent. Except for the reaction of cyclopentene with $\text{1a}$ all other olefins used, react with vinyl cation $\text{2}$ to form the cycloaddition products $\text{7}$, $\text{8a}$ and $\text{8b}$ in high yields.     

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.     

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> $\text{2b}$/$\text{1b}$).