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> $\text{2b}$/$\text{1b}$).     

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 $\text{7}$.     

New tetrahydropyrans from a marine sponge

Two new tetrahydropyrans have been isolated from the sponge Haliclona sp. From chemical and spectroscopic evidence they are shown to be (1′$\text{R}$, 2$\text{S}$, 2″$\text{E}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromethyl)-2,5-dimethyl-6-(penta-2″,4″-dienyl)-tetrahydropyran and (1′$\text{R}$, 2$\text{S}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromoethyl)-2,5-dimethyl-6-(pent-4″-enyl)-tetrahydropyran.     

Kalashine,a novel type aporphine-benzylisoquinoline alkaloid

$\text{Berberis orthobotrys}$ produces the new dimer kalashine ($\text{1}$), together with the previously reported pakistanamine ($\text{2}$) and pakistanine ($\text{3}$). Kalashine is the first aporphine-benzylisoquinoline known to be substituted at C-11. Acid catalyzed rearrangement of pakistanamine ($\text{2}$) in 3N HCl leads to 1-0-methylpakistanine ($\text{6}$) together with small amounts of 1-0-methylkalashine ($\text{7}$) and (+)-armepavine ($\text{8}$). Rearrangement of $\text{2}$ using methanol containing a little 3N HCl gives about equal amounts of $\text{6}$ and 1,10-di-O-methylpakistanine ($\text{9}$).     

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 $\text{1}$.     

An example of a novel synthetic approach to alkenylpyrroles

The synthesis of 2-methyl-3-(2-propenyl)pyrrole ($\text{2}$) and E- and Z-2-methyl-3-(1-propenyl)pyrroles ($\text{3}$) via the reaction of 3-butenyl methyl ketoxime ($\text{1}$) with acetylene in the KOH-DMSO system is reported.     

Synthesis with an immobilized enzyme of N-acetyl-9-O-acetyl-neuraminic acid,a sugar reported as a component of embryonic and tumor antigens.

Condensation of 2-acetamido-6-$\text{O}$-acetyl-2-deoxy-D-mannose with pyruvic acid in the presence of immobilized acylneuraminate pyruvate lyase (2.8 units) gave 5-acetamido-9-$\text{O}$-acetyl-3,5-dideoxy-D-$\text{glycero}$-D-$\text{galacto}$-2-nonulopyranos-1-onic acid ($\text{N}$-acetyl-9-$\text{O}$-acetylneuraminic acid) on the 0.3 mmole scale.     

Conversion of adenosine to a pentacyclic structure by a 4-nitroquinoline-1-oxide metabolite model.

A new pentacyclic compound $\text{2A}$ has been obtained from the reaction of adenosine $\text{1}$ with 1-acetoxy-4-(acetoxyimino)-1,4-dihydroquinoline $\text{3}$, a model for the ultimate metabolite of the carcinogen 4-nitroquinoline-1-oxide. 9-propyladenine $\text{5}$ gives an analogous pentacyclic product $\text{6A}$ whose crystal structure has been determined.     

The formation and subsequent cyclisation of novel hydroperoxides from a 1,4− and a 1,5-diene

The preparation of the unsaturated hydroperoxides ($\text{3}$,$\text{4}$,$\text{5}$,$\text{6}$ and $\text{7}$) by the sensitized photooxidation of the 1,4-diene($\text{1}$) and the 1,5-diene($\text{2}$) is described, together with the attempted free-radical cyclisation of these.     

The quettamines: a new class of isoquinoline alkaloids

Three quettamine type alkaloids, which incorporate either a benzofuran or a dihydrobenzofuran moiety within the molecular framework, have been obtained from $\text{Berberis}$$\text{baluchistanica}$. These are dihydrosecoquettamine ($\text{1}$), secoquettamine ($\text{2}$), and quettamine chloride ($\text{3}$). Alkaloids $\text{1}$ and $\text{3}$ are racemates. Hofmann degradation of quettamine ($\text{3}$) provides secoquettamine ($\text{2}$) and the styrene $\text{4}$ which has a trans relationship between the hydrogens at C-1 and C-α, thus indicating the identical stereochemistry in quettamine. Emde reduction of quettamine leads to dihydrosecoquettamine ($\text{1}$) and the stilbene $\text{5}$. Two other polar alkaloids in the plant are (+)-armepavine methochloride ($\text{6}$) and oblongine chloride ($\text{7}$). An oblongine type alkaloid must be the biogenetic precursor for the quettamines. Arguments are presented favoring direct oxidative coupling in the biogenesis of the cularine alkaloids.     

Completely stereoselective synthesis of all four stereoisomeric 1-carbamoyloxy-1,3-alkadienes via anti-diastereoselective homoaldol reaction from aldehydes and a single carbon-three-unit

Lithiation of both ($\text{Z}$)- and ($\text{E}$)-3-trimethylsilyl-2-propenyl $\text{N}$,$\text{N}$-diisopropyl carbamate 2 affords the (2$\text{E}$) -lithium compound 3. Aluminium- or titanium-mediated addition to aldehydes, 4 gives (1$\text{E}$)-(3$\text{R}$*4$\text{S}$*)-enol carbamates 7. A stereospecific Peterson elimination (borontriflouride- or base-mediated) introduces the second double bond either with (3$\text{E}$)- or with (3$\text{Z}$)-configuration. So just by reagent selection for each of the two steps, (1$\text{E}$,3$\text{E}$)-, (1$\text{E}$,3$\text{Z}$)-, (1$\text{Z}$,3$\text{E}$)-, or (1$\text{Z}$,3$\text{Z}$)- dienes 8 - 11, respectively, are prepared with stereoselectivities up to > 99.7%     

A 1,2-phenyl shift to the double bond of a vinyl cation

Reaction of HCl with 3-phenylpropyne ($\text{1}$) afforded 1,2-dichloro-2- phenylpropane($\text{6}$) among other products. The reaction proceeds by a 1,2-phenyl shift to the 5-phenyl-1-propene-2-yl cation ($\text{2}$).     

Revision of the structure assigned to a monoterpene isolated from Piqueria trinervia

Unambiguous synthesis of 2-methyl-3-isopropenylanisole ($\text{1}$) and 2-isopropenyl-3-methylanisole ($\text{4}$) has led to revision, from ($\text{1}$) to ($\text{4}$), of the structure assigned to a monoterpene phenol ether isolated from $\text{Piqueria trinervia}$.     

Synthetic studies of trichothecenes,an enantioselective synthesis of a C-ring precursor of anguidine

An enantioselective synthesis of a cyclopentanoid C-ring precursor $\text{1}$$\text{9}$ of anguidine $\text{3}$, a representative trichothecene with antitumor activity, from 2-allyl-2-methylcyclopentane-1,3-dione is described.     

(4+2)-cycloaddition of nitroalkenes with ynamines; formation of a 4H-1,2-oxazine 2-oxide derivative

The formation of a thermally unstable (4+2)-cycloadduct, a 4H-1,2-oxazine 2-oxide derivative ($\text{1}$), from the reaction of 1-nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene has been proven by the structure elucidation of isoxazole derivative $\text{3}$ which results from thermal rearrangement and by the structure determination of the 1,3-dipolar adducts $\text{5}$ of $\text{1}$ with electron-deficient acetylenes.     

Synthesis and crystal structure of a π-allyl iron carbonyl complex derived from a fluorocarbon containing ligand by loss of fluorine

The β-chlorovinylphosphines R₂P$\text{C  CCl(C}$F₂)₃ (R = C₆H₅, C₆H₁₁) react with Fe(CO)₅ yielding compounds of stoichiometry

. The crystal structure of one of these (R = C₆H₁₁) has been determined from X-ray diffraction data and refined by least-squares to $\text{R}$ = 0.037 (2313 reflections with $\text{I}$ > 2.3σ_$\text{I}$). Crystals are triclinic, space group $\text{P}$$\text{1}$, $\text{a}$ = 10.253(5), $\text{b}$ = 15.590(7), $\text{c}$ = 9.390(4)Å, α = 99.88(3), β = 103.21(2), γ = 92.02(2)°, $\text{Z}$ = 2. The fluorinated π-allyl group is σ-bonded to one Fe atom and π-bonded to the other.     

On the stereochemistry of an alkylcuprate induced conversion of a bromoallene into an alkylallene

By preparing $\text{levorotatory}$$\text{2}$ following a route of known stereochemistry, we were able to elucidate the stereochemistry of the conversion of the levorotatory bromoallene $\text{1}$ into levorotatory $\text{2}$ by $\text{t}$-Bu(CN)CuLi: the reaction occurs with retention of configuration in the allenyl moiety.     

Structure of aszonalenin,a new metabolite of aspergillus zonatus

Aszonalenin ($\text{1}$) has been isolated from $\text{Aspergillus zonatus}$ together with LL-S490β ($\text{2}$) and the structure of $\text{1}$ has been established by spectroscopic evidences and chemical transformation.     

Photolysis of a 2-tetbazeio from an enehydrazine

Photolysis of the 2-tetrazene $\text{1}$ gives the triazole $\text{2}$ by homolysis of one single N,N-bond. The formation of the other products $\text{4}$ – $\text{13}$ can be rationalized by regarding the aza-allyl radical $\text{3}$ as a common precursor.