A spirocyclic chroman from a spiroepoxycyclohexadienone

Reaction between the hydroxymethylspiroepoxycyclohexadienone ($\text{2}$) and chlorotrimethylsilane gave the spirocyclic chroman ($\text{3}$) whose crystal structure has been determined. The chroman presumably arose by dimerisation of an intermediate $\text{o}$-quinone methide ($\text{5}$). The stereochemistry of the chroman ($\text{3}$) in solution is also considered.     

Phosphazene spirannique a partir de derives du phophore dicoordine

The reaction of azidoalcohol $\text{2}$ on triazaphosphole $\text{1}$ takes place according to pathway $\text{a}$ and not $\text{b}$, as shown by the isolation of spirannic phosphazene $\text{3}$. The diazadiphosphetidines $\text{4}$, dimers of $\text{3}$ are also caracterized.     

Potential bile acid metabolites. 1. The epimeric 3ϵ,7α,12β-trihydroxy-5β-cholanic acids. Raney nickel as an epimerizing catalyst.

The epimeric 3α,7α,12β- and 3β,7α,12β-trihydroxy-5β-cholanic acids have been prepared. Under ambient hydrogenation conditions with Raney nickel as catalyst the axial 3β-ester ($\text{4b}$) is epimerized to the 3α-compound ($\text{2b}$).     

Khyberine and the biogenesis of dimeric aporphine-benzylisqoquinoline alkaloids

The new aporphine-benzylisquinoline khyberine ($\text{4b}$) is present in $\text{Berberis}$$\text{calliobotrys}$ Aitch. ex Bienert in about one part per million. An effort is made to present a complete scheme for the biogenesis of aporphine-benylisoquinoline dimers which arise from the condensation of two coclaurine units.     

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 synthesis of γ-fluoroisoleucine

Condensation of 3-fluoro-2-butanone ($\text{2}$) with alkyl diethylphosphonoacetates ($\text{4a–d}$) gave alkyl 4-fluoro-3-methyl-2-pentenoates ($\text{5a–d}$). Addition of bromine yielded alkyl-2,3-dibromo-4-fluoro-3-methylpentanoates ($\text{6a,b}$) which were dehydrobrominated to alkyl 2-bromo-4-fluoro-3-methyl-2- pentenoates ($\text{7a,b}$). Since these compounds could not be hydrogenated to the desired alkyl 2-bromo-4-fluoro-3-methylpentanoates ($\text{8a,b}$), another route was taken. The esters $\text{5a–d}$ were hydrogenated to alkyl 4-fluoro-3- methylpentanoates ($\text{11a–c}$) which were converted to their carbanions. Treatment with bromine gave esters $\text{8a–c}$, and iodine gave alkyl 4-fluoro-2-iodo- 3-methylpentanoates ($\text{12a,b}$). Esters $\text{8a–c}$ and $\text{12a,b}$ were converted to alkyl 2-azido-4-fluoro-3-methylpentanoates ($\text{13a–c}$) whose hydrogenation gave alkyl 2-amino-4-fluoro-3-methylpentanoates ($\text{14a–c}$). Hydrolysis afforded γ-fluoroisoleucine ($\text{1}$).     

Synthesis of 3-methylisoguanosine,a positional isomer of pharmacologically active nucleosides from marine animals

3-Methylisoguanosine ($\text{4c}$) has been synthesized from 5-(cyanomethylamino)-1(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)imidazole-4-carboxamide ($\text{1b}$) through the carbonitrile ($\text{2b}$).     

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.     

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 ($\text{4b}$).     

Total syntheses of (±)-isoagatholactone and (±)-12α-hydroxyspongia-13(16),14-dien

(±)-Isoagatholactone $\text{1}$ and (±)-12α-hydroxyspongia-13(16),14-dien $\text{2b}$, a fundamental skeleton of spongiadiol $\text{2a}$ and its congeners, have been synthesized from (±)-labda-8(20),13-dien-15-oic acid $\text{3}$.     

Isolation of a crystalline thiete and its ‘open’ isomer; Photoproducts of xanthenethione and bis(tert-butylthio)ethyne

Irradiation of xanthenethione $\text{1}$ with bis(tert-butylthio)ethyne $\text{2}$ yielded both the expected α,β-unsaturated dithioester $\text{4b}$ and surprisingly its proposed intermediate thiete $\text{3b}$ as crystalline compounds. In solution an equilibrium between both compounds has been observed.     

Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

cleavage of the epoxide ($\text{2}$) of methyl (-)-kaur-9(11)-en-19-oate ($\text{1b}$) with boron trifluoride-ether in benzene and in acetic anhydride yielded ($\text{3a}$) and ($\text{3b}$), respectively. On epoxidation with $\text{m}$-chloroperbenzoic acid in the presence of $\text{N}$-nitrosomethyl urea, ($\text{1b}$) suffered a backbone rearrangement to form ($\text{6}$).     

The clemmensen reaction of tigogenin. A reinvestigation

The reaction of tigogenin ($\text{1b}$) with amalgamated zinc yields tetrahydrotigogenin ($\text{2b}$) and the furostan $\text{3}$. While $\text{2b}$ undergoes acid catalyzed elimination to give the rearranged product $\text{7}$, $\text{3}$ spontaneously decomposes to a mixture of $\text{4}$ and $\text{5}$.     

Self-condensation of 1,3,4,6-tetraketones. The electrocyclic reaction of a dienone system derived from the dienolic form.

A synthesis of dihydropyrones $\text{4}$ is described involving the dimerisation of tetraketones $\text{1}$ and thermal reaction of intermediate dienone $\text{2}$ derived from a dienolic system.     

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> $\text{2b}$/$\text{1b}$).     

Efficient photochemical oxetane formation from 1-methyl-2,4,5-triphenylimidazole and benzophenones

In contrast to simple imidazoles, 1-methy1–2,4,5-triphenylimidazole ($\text{1}$) produced stable oxetane photoadducts $\text{3b}$ - $\text{e}$ with good efficiency upon irradiation in the presence of benzophenone derivatives $\text{2b}$ - $\text{e}$ in acetonitrile solution. Irradiation in the solid-phase was also studied. The oxetanes $\text{3b}$ - $\text{e}$ readily underwent cycloreversion by acid catalysis or by heating.     

Novel fluoride transfer in the reaction of tricyclic epoxides with boron trifluoride

Reaction of the tricyclic epoxides ($\text{1a}$) and ($\text{1b}$) with boron trifluoride etherate leads to fluorohydrins ($\text{2a}$) and ($\text{2b}$) derived in the novel fluoride transfer, whereas ($\text{1c}$) undergoes isomerization to spiro ketone ($\text{3}$).     

An efficient synthesis of optically pure anthracyclinone intermediates by the novel use of microbial reduction

Reduction of the racemic α-hydroxy ketones((±)-$\text{3a,b}$) with fermenting baker's yeast followed by fractional recrystallization and oxidation was found to readily afford optically pure anthracyclinone intermediates((R) (?)-$\text{3a,b}$ and their partially optically active antipodes ((S)(+)-$\text{3a,b}$). The useless enantiomers ((S)(+)-$\text{3a,b}$ and diastereomeric $\text{vicinal}$-diols((+)- $\text{5a,b}$) could be recycled to (±)-$\text{3a,b}$ and the achiral ketones($\text{6a,b}$) by racemization and oxidative cleavage, respectively.     

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.     

Biomimetic synthesis of bacterial c50 carotenoids decaprenoxanthin and c.p. 450

Alkylation of the distal double bond of pseudoionone $\text{4}$ has been carried out with isoprene epoxide (ZnCl₂ /MeNO₂ ) leading directly to α-$\text{cis 10 a}$, α-$\text{trans}$$\text{10b}$ and γ $\text{10c}$ hydroxyprenylionones. The α-$\text{cis}$ and γ-isomers have been converted in few steps into the C₅₀ carotenoids decaprenoxanthin $\text{1}$ and C.p. 450 $\text{3}$ respectively.