Rearrangement spinal en serie a/b cis : conversion du lithocholate de methyle en derives du d-homoandrostane

A new backbone rearrangement is observed in A/B $\text{cis}$ methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters $\text{1}$ by AgSbFg₆ or by the action of the triflic anhydride on the si1y1ated ether $\text{2}$. This rearrangement leads to methyl diacholenate $\text{3}$ and new lactones in D-homoandrostane series $\text{5}$ and $\text{6}$. The differences of behaviour between A/B $\text{cis}$ and A/B $\text{trans}$ series and the mechanism of rearrangements are discussed.     

Nitroindolenines en serie vincadifformine : intermediaires d'acces a la vincamone et a un squelette azahomoaspidospermane

Vincadifformine and its 10-substituted analogs give in good yields 16-nitro indolenines of which the reactivity has been studied. By a two step process (demethoxycarbonylation and chloration on C16) nitro-indolenine $\text{2b}$ leads to gem-chloro-nitro $\text{6}$. By an other two step sequence (NaBH₃CN, NaH) nitro-indo-lenine $\text{2c}$ yields compound $\text{10}$ via a 16 → 1 COOCH₃ migration. By heating compounds $\text{6}$ and $\text{10}$ in CF₃COOH, rearranged products are obtained : vincamione $\text{5}$ from $\text{6}$ and azahomoaspidospermane $\text{13}$ from $\text{18}$. Mechanisms of formation of $\text{5}$, $\text{10}$ and $\text{13}$ are discussed.     

The reaction of 2-azaallenium salts with carbodiimides and tert-butyl isocyanide

2-Azaallenium salts $\text{1}$ react with diisopropyl carbodiimide to afford the formal dihydro-1,3-diazetium salts $\text{5}$. The structure of $\text{5c}$ has been confirmed by an X-ray diffraction analysis. With the carbodiimide $\text{2e}$ the tetraphenyl-2-azaallenium salt $\text{1a}$ reacts to give the guanidinium compound $\text{6}$.The diazetium salts $\text{5}$ react with further carbodiimide to afford the formal 2-azaallenium salts $\text{11}$. With tert-butyl isocyanide the 2-azaallenium salts $\text{1}$ undergo an Ugi reaction to yield the nitriles $\text{14}$.     

Synthesis of O-6-alkylated deoxyguanosine nucleosides

A general route for synthesis of 6-$\text{O}$-alkyl-2∝deoxyguanosine nucleosides is described. The key step is conversion of the 6-$\text{O}$-TPS derivative $\text{2}$ to the 6-trimethylamino compound $\text{3}$. The trimethylamino group is readily displaced by alcohols in the presence of DBU. Using this route the 6-$\text{O}$-methyl, ethyl and n-butyl 2∝-deoxyguanosine derivatives $\text{5a-c}$ have been prepared in excellent overall yields.     

2,2-(n,n′-dimethyl-ethylendiamino)-ethylendiazonium-ion,ein diazonium-ion mit ungewöhnlichen eigenschaften

On treating with potassium methoxide at room temperature the donor-substituted ethylenediazonium ion $\text{2}$ equilibrates with the stable α-diazoolefin $\text{3}$. At the same temperature the reaction of $\text{2}$ with dilute methanesulfonic acid leads to a quantitative elimination of diazo nitrogen. Finally the 1,3-dipolar cycloaddition of $\text{2}$ to dimethyl acetylenedicarboxylate affords the pyrazole derivative $\text{5}$ in high yield.     

Reactions of cyclo-octatetraene and its derivatives - X: 1,2,3,8-Tetraphenylcyclo-octatetraene and 2,3,4,5-tetraphenylcyclo-octa-1,3,5-triene

The reaction of tetracyclone $\text{1b}$ with the cyclo-octatetraene-dimethyl acetylenedicarboxylate adduct $\text{2}$ at $\text{ca}$. 110° produces, in addition to the $\text{exo}$[4+2] Π cycloadduct $\text{3b}$ (49%), 1,2,3,8-tetraphenylcyclo-octatraene $\text{5}$ (11%), together with the diketone $\text{11}$ (5%). In a similar reaction with the esterified cyclo-octatetraene-maleic anhydride adduct $\text{13a}$, the major product $\text{14}$ (82%) is accompanied by the cyclohexa-1,3-diene $\text{15}$ and the dihydrosemibullvalene derivative $\text{16}$. Thermolysis of $\text{3b}$ at $\text{ca}$. 145° leads to the cyclobutene $\text{12}$., which on catalytic hydrogonation followed by decarbonylation at 180°–190° gives 2,3,4,5-tetraphenylcyclo-octa-1,3,5-triene $\text{19}$. Attempted thermal conversion of $\text{19}$ into a dihydrosemibullvalene failed.     

H3N·PF5 and H2NPF5−, new compounds in the system H3N/PF5

Phosphorus pentafluoride was reported long ago to give adducts 2 PF₅ ·5 NH₃ (1) and nNH₃·PF₅ (n= 1 ? 4) (2). None of the compounds was characterised in detail. Repeating the reaction of PF₅ and NH₃ we found the adduct H₃N·PF₅, $\text{1}$, in 8% yield besides (H₂N) ₂PF₃ (3) and NH₄PF₆. However, HF and (F₂P=N)₃ gave $\text{1}$ in 41% yield. The ¹H, ¹⁹F, and ³¹P n.m.r. spectra of $\text{1}$ exhibit ¹⁴NH, ¹⁴NPF(cis), and ¹⁴NP coupling. The x-ray structure determination shows almost perfect octahedral geometry at phosphorus with a PN bond length of 1.842 ā. Compound $\text{1}$ is soluble in water without decomposition. Treatment with NH₃ leads to the anion H₂NPF₅^?. Upon heating $\text{1}$ forms in good yield H₂NPF₄ and NH₄PF₆. Without a solvent $\text{1}$ and NH₃ react to give (H₂N) ₂PF₃. A mechanism for the ammonolysis of PF₅ is proposed.     

Per - bicyclophosphoranylation d'alditols

Reaction of bicyclophosphane $\text{1}$ with glycol $\text{2}$, glycerol $\text{3}$, erythritol $\text{4}$, L(-)arabitol $\text{5}$ and dulcitol $\text{6}$ leads to the corresponding per-alkoxybicyclophosphoranes $\text{2p}$ - $\text{6p}$ which are in tautomeric equilibrium with the phosphates forms $\text{2p}$′ - $\text{6p}$′.The amount of these latters increases regularly from traces to 24%.     

Photocyclisierung eines gibberellinaldehyds zu epimeren cyclobutanolen und deren basische rückspaltung partialsynthese von 16,17-dihydro-Δ15-gibberellin-A3

UV-irradiation of the aldehyde $\text{1}$ leads to the 7-epimeric cyclobutanols $\text{2a}$ and $\text{2b}$ which undergo upon treatment with NaOCH₃ retroaldol-like cleavage to $\text{1}$ and $\text{3}$. Oxidation and deacetylation of $\text{3}$ affords the 16,17-dihydro-Δ¹⁵-gibberellin-A₃ ($\text{5}$).     

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.     

A route to Prelog-Djerassi lactone from methyl α,D-glucopyranoside

The enone $\text{1}$ obtained from methyl α,D-glucopyranoside is converted into the corresponding diene $\text{5}$ which is hydrogenated to give predominantly the diequatorial dimethyl hexopyranoside $\text{3}$. C6 of the latter is converted stepwise to the methyl ketone from which Prelog-Djerassi Lactone $\text{8}$ and its 2-epimer $\text{9}$ are prepared in 3:2 ration.     

Vinylic carbanions in synthesis. Novel syntheses of iso-gregatin B,iso-aspertetronin A and related O-methyl tetronic acids

Reaction between the octadienone (8) and the vinylic carbanion (6) derived from (5) leads, in one step, to the O-methyl tetronic acid (9). Metallation of (9), followed by treatment of the resulting α-vinylic carbanion with methyl acetate and with methyl $\text{E}$-butenoate then gives the acylated O-methyl tetronic acids (12) and (14) respectively which are shown to be enol ether isomers of the natural products gregatin B and aspertetronin A found in $\text{Aspergillus sp}$. and $\text{Cephalosporium gregatum}$.     

An unusual rearrangement of eudesmane skeleton

The lactone $\text{5}$ was found to be a co-product of the BF₃ etherate induced cyclization of epoxyisogermacrone $\text{2}$. The keton $\text{3}$ when treated with 100% HCOOH afforded the lactone $\text{5}$ while under the same conditions the ketol $\text{4}$ gave the corresponding ester $\text{6}$. A mechanism is suggested for the rearrangements.     

On the stereochemistry of photoaddition between α,β-unsaturated ketones and olefins. III.

The α,β-unsaturated ketone $\text{1}$ yields with allene the photocycloadduct $\text{3}$ predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence $\text{1}$ → $\text{4}$ → $\text{5}$ → $\text{6}$ → $\text{7}$. The isomeric ketone $\text{2}$ is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked.     

Synthesis of streptococci phosphatidyl-α-diglucosyldiglyceride and related glycolipids : Application of the tetraisopropyldisiloxane-1,3-diyl (tips) protecting group in sugar chemistry. Part V

A short and convenient synthesis of phosphatidyl-α-diglucosyldiglyceride (i.e. compound $\text{8d}$) and two related Streptococci glycolipids (i.e. compounds $\text{6a}$ and $\text{6b}$) will be presented. 4',6'-Tetraisopropyl-disiloxane-1,3-diyl (TIPS) protected α-glucosyl diglyceride (i.e. compound $\text{2}$) turned out to be a suitable protected precursor. Thus, compound $\text{2}$ was selectively condensed with glucosyl bromide $\text{3}$ to afford $\text{4}$. Removal of the protecting groups from $\text{4}$ gave glycolipid $\text{6a}$. The “dynamic” properties of the TIPS pro- tecting group were utilized to convert 4',6'-TIPS protected $\text{4}$ into 3',4'- TIPS protected derivative $\text{5a}$. Compound $\text{5a}$ could then be condensed with either a stearoyl fatty acid or a phosphatidyl moiety to give the fully protected derivatives $\text{5c}$ and $\text{8a}$, respectively. Finally, removal of all the protecting groups from $\text{5c}$ and $\text{8a}$ afforded the glycolipid $\text{6b}$ and glycophospholipid $\text{8d}$, respectively.     

Directive effect of β-functionalization on the regiochemistry of the base induced homoketonization of bridgehead substituted 1,3-bishomocubane acetates

Base induced homoketonization of bridgehead acetate $\text{6}$ leads to the thermodynamically favored half cage skeleton $\text{7}$, whereas cage opening of $\text{5}$ is directed by the β-ketofunction to give cleavage of the central C₅–C₆ bond producing half cage diketone $\text{10}$.     

Preparation of some highly halogenated derivative of furan

Direct chlorination of 2-(2H-hexafluoropropyl)-tetra- hydrofuran $\text{1}$ gave high yield of 2-(2-chlorohexafluoropropyl)- pentachloro-2,5-dihydrofuran $\text{2}$. Bromination of $\text{1}$ gave very complex mixture of products, from which three compounds, $\text{viz}$. 2-bromo-5-(2H-hexafluoropropyl)-furan $\text{3}$, 3-bromo-5-(2H-hexafluoropropyl)-furan $\text{4}$, and 2,4-dibromo-5-(2H-hexafluoropropyl)furan $\text{5}$ were isolated. Exchange fluorination of $\text{2}$ with dry KF at 240 – 300° led to a stepwise substitution of fluorines for chlorines to give mixtures of chloro-fluoro-2-(2-chlorohexafluoropropyl)-dihydrofurans $\text{7}$,$\text{8}$,$\text{9}$ and $\text{10}$, together with small amounts of 2-(2-chlorohexafluoropropyl)-3,4,5-trichlorofuran $\text{6}$.Exchange fluorination of 3,4-dihalo-2,2,5,5-tetrafluoro- 2,5-dihydrofurans $\text{11a}$ and $\text{11b}$ led to a substitution of fluorine for one vinylic halogen to give 3-halo-2,2,4,5,5-pentafluoro-2,5-dihydrofurans $\text{12a}$ and $\text{12b}$ in good yields.Compounds $\text{2}$ – $\text{12}$ were characterised by n.m.r., m.s., and i.r. spectroscopy and elemental analysis.     

Synthesis and crystal structure of 1,1,1,5,5,5-hexafluoro-2-aminopentan-4-one (HFAP)

The vapour phase reaction of ammonia and hexafluoroacetylacetone leads to the formation of the new β-keto-amine C₅H₃F₆NO. Crystals of the compound are monoclinic, space group $\text{P}$2₁/$\text{n}$, $\text{a}$ = 10.01(2), $\text{b}$ = 19.33(3), $\text{c}$ = 8.40(1) Å, β = 82.27(6)°; final R = 0.044.     

Triplet-mediated coupling of 5-bromo-1,3-dimetrhyluracil to Nb-methoxycarbonyltryptamine involving a double electron transfer

On acetone-sensitization, 5-bromo-1,3-dimethyluracil ($\text{1}$ reacts with N^b-methoxycarbonyltryptamine ($\text{4}$ under the assistance of an electron carrier such as 2-methoxynaphthalene to give a coupling product $\text{6}$. A mechanism involving a double electron transfer via the triplet state of $\text{1}$ is proposed.     

On the stereoselectivity of the α-alkylation of β-hydroxy esters. Enantioselective synthesis of 4,4- and 6,6-disubstituted cyclohex-2-en-1-ones.

Stereoselective α-alkylation of the optically active 6-hydroxyester $\text{1}$ gives rise to $\text{2}$, which was converted to the 1,5-diketone $\text{4}$. Regioselective aldolcondensation of the latter furnished (S)-$\text{5}$ and (S)-$\text{6}$ respectively, each with an e.e. of 86%.