Regioselective Friedel-Crafts acetylation of 5-hydroxyindole derivatives: synthesis of 4H-pyranoindol-4-one derivatives

The Friedel-Crafts acetylation of 5-hydroxyindole derivativesla-c regioselectively produced 6-acetyl-5-hydroxy-indole derivatives2a-c which were condensed with cinnamic acid using POC1₃ and dry pyridine to afford 5-cinnamoyloxy-6-acetyl-indoles3a-c. These upon Baker-Venkataraman transformation furnished 6-cinnamoylacetyl-5-hydroxyindoles4a-c which were cyclised separately with AcOH/HCl and Ac₂O/AcONa to 4H-pyrano-(2,3-f)indol-4-one derivatives5a-c and6a-c respectively.     

Synthesis of methanethial s-oxide (sulfine) and alkanethial s,s-dioxides by fluorodesilylation. Stereochemistry of their cyclopentadiene diels-alder adducts

Fluorodesilylation of trimethylsilylmethanesulfinyl chloride 4 in the presence of cyclopentadiene gives 2-thiabicyclo[2.2.1]hept-5-ene endo-2-oxide,5; in a like manner 1-trimethylsilylalkanesulfonic anhydrides afford endo- and exo-3-alkyl-2-thiabicyclo[2.2.1]hept-5-ene 2,2-dioxides, with the endo isomer predominating. Sulfine and alkyl sulfenes are invoked.     

New synthesis of steroidal tetrahydrooxazin-2-ones

In the DMSO/NaHCO₃ system, 16α-aminomethyl-, 16α-benzylaminomethyl- and substituted benzylaminomethyl-3-methoxy-17β-tosyloxyestra-1,3, 5(10)-triene (3, 5a-k) do not undergo oxidation, but form a tetrahydrooxa-zin-2-one ring (7, 8a-k) via neighboring group participation. Under similar conditions, 16β-aminomethyl-3-methoxy-17β-tosylestra-1,3,5(10)-triene (4) decomposes into 16-methylene-3-methoxyestra-l,3,5(10)-trien-17-one (12).     

Synthesis of 3-methyl-coumarins, -thiacoumarins and -carbostyrils

Reaction of 3,6-dimethyl-4-phenyl-3,4-dihydrocoumarin5a with anhydrous aluminum chloride gave 3,6-dimethyl-coumarin (6a); likewise, 6-chloro-3-methyl-coumarin (6b) was obtained from5b. Substituted 3-methyl-thiacoumarins (8a,b and 3-methyl-carbostyrils (10a-e) were prepared from the reactions of the respectivea-methyl-cinnamoyl derivatives (7a,b and (9a-e), of thiophenols and anilines.     

A General Method for Stepwise Elongation of the (1→5)-α-D-Arabinofuranan Chain

Condensation reaction of 3,5-di-O-benzoyl-1,2-O-(1-cyanoben-zylidene)-β-D-arabinofuranose (2) with benzyl and allyl 2,3-di-O-benzoyl-5-O-triphenylmethyl-α-L-arabinofuranosides (5a and 5b) in methylene chloride in the presence of triphenylcarbenium tetrafluoroborate as catalyst under high vacuum gave α-(1→5)-linked dimeric D-arabinofuranoside derivatives (6a and 6b). One of the dimeric compounds (6a) was debenzoylated, triphenylmethylated, and rebenzoylated to give a dimeric homolog of 5a (8). Similarly for the preparation of 6a, 8 was condensed with 2 to provide an α-(1→5)-linked trimeric D-arabinofuranoside derivative (9). Further elongation of the glycoside chain might be possible in the same way.     

Determination of stereostructure of naturally occurring α, β-unsaturated δ-lactone derivatives through a stereoselective synthesis

The stereostructures of (Z)-tarchonanthuslactone (2) and the δ-lactone of (Z)-5, 7, 9, 11-tetrahydroxyhexacos-2-enoic acid (3) were established as9 and27 by the stereoselective syntheses of authentic9 and26 (triacetate of3), respectively.     

A 270 MHz 1H-NMR study of three “branched” ribonucleotides A2'p5'U3'p5'g,A2'p5'C3'p5'G and A2'p5'G3'p5'G the importance of being branched with a 2'→5' phosphodiester bond in the pre-mRNA processing reactions (splicing)

Conformational studies with three analogues 3, 4 and 5 of naturally-occurring branched ribonucleotides 1 and 2 have shown that they adopt a secondary structure which is overwhelmingly controlled by a stacking between adenine(2' → 5')nuc1eobase residues while the 3' → 5' linked guanine residue is apart. This observation along with the fact that all four nucleosides can form lariats in nuclear mRNA splicing, but it is guanosine as the 2' → 5' nucleotide that can drive the splicing reaction to completion, suggests a biological significance of the additional 2' → 5' phosphodiester bond formation in the splicing reaction. It is likely that the final implication of formation of such a 2' → 5' linked lariat is that it provides a pathway to assume a free energy minimum conformation through the 2' → 5' stacking, especially in the case of guanosine, to drive the splicing reaction to completion (stacklng-driven-energy-pump).     

A novel short and efficient asymmetric synthesis of statine analogues

The statine analogues 1a–c have been obtained in high optical purity via addition of the chiral acetate enolate 4 to the α-aminoaldehydes 5a–c, followed by transesterification.     

SIMS and AES measurements on the LaNi5-hydrogen system

Summary SIMS (Secondary Ion Mass Spectrometry) and AES (Auger Electron Spectroscopy) investigations were carried out on polycrystalline LaNi₅ samples and on LaNi₅ samples, which have been loaded with hydrogen electrochemically. AES measurements show an enrichment of obviously oxidized La at the surface, while in the SIMS spectra the emission of negative ions attracts special attention. In contrast to the V-H- and Nb-H-system negative Me_xH_y-ions turned out to be the most sensitive species for hydrogen detection in SIMS experiments on LaNi₅. The emission of negative ions of type Ni_x and Ni_yH_x, which are not observed on pure Ni are due to the electropositive character of La in this special matrix and the presence of hydrogen. The results point to a higher affinity of hydrogen to Ni than to La.     

Are all charge-repulsed carbocations really unstable? Dramatic difference in reactivities of benzyl- and p -methoxybenzyl halides in benzene

Two distinct reaction mechanisms are proposed for the reactions of1,5 and6 with nucleophiles as against those of11,12 and16. The former set undergoes the reactions through carbocation type intermediates2 and3 as efficiently as the stable carbocation4 does, even under similar and very mild conditions. The compounds from the latter group do not form the carbocations under the same conditions and undergo only direct substitution by strong nucleophiles.     

Surprising reactions or special azoolefins - self-arylation,indole ring closure,mild chlorine substitution,and “tert. amino effect”

Azoolefins 2 either decompose or react with aryldiiminea with uptake of an aryl group to give compounds 3. The latter can undergo ring closure to N-amino-indoles 4. In the 2,4,6-trichloro compound 3bortho-chlorines are selectively replaced bymorpholine under very mild conditions giving 5a, which easily fragments to form the benzimidazole 7.     

An allylic nucleophilic substitution reaction of 1α-hydroxyvitamin D derivatives

The first transformation of the 5,6- trans-vitamin D conjugated triene system into that of isovitamin D occurring under nucleophilic conditions is observed in the reaction of 5 with n-butyl-lithium to give 6.     

Uncatalyzed insertion reaction of isocyanides into a carbon-sulfur bond

Tert-butylisocyanide and tert-octylisocyanide insert into the carbone-sulfur bond of activated sulfides 2 yielding thioimidates 5 which rearrange to enamines 6.     

Dioscorone. Regioselective Oxxmercuration of 2-Azabicyclo[2. 2]oct-5-ene

Oxymercuration of 2-azabicylo[2.2.2]oct-5-ane 1 occurs regioselectively to give a50:50 mixture of 5-syn-and 5-anti-isoquinculidinols 2 which can be converted to dioscorone 5.     

Formation of a bis-lactone from 3-O-acetyl-deoxycholic acid

By the action of dichloroethyl phosphate upon 3α-acetoxy-12α-hydroxy-5β-cholanic acid (1) in methylene chloride, unexpectedly, a bis-lactone2 was formed. Sodium methoxide catalyzed deacetylation of2 afforded 16-membered deoxycholic acid 24, 12'α: 24′, 12α-bis-lactone (3) whose structure was determined by an x-ray structural analysis.     

Nouvelle synthese des benzodiazepines-1,5 a partir de la γ-pyrone

Reaction of 0-phenylenediamines 2, 3 with 2-hydroxy-6-methyl-4-pyrone leads to:2-butoxycarbonylmethylene-4-methyl-1,5-benzodiazepines 4, 5, 4-acetylmethylene-1,5-benzodiazepin-2-ones 6, 7, and benzimidazoles 8, 11. These compounds results from competitive reactions and different ways of cyclization.     

Alkaline degradation of the mycotoxin 4-deoxynivalenol

Treatment of the Fusarium trichothecene mycotoxin 4-deoxynivalenol (1) (DON)with aqueous NaOH at 75°C gave a mixture of three isomeric degradation products designated norDON-A (3a), norDON-B (4a) and norDON-C (5a). Structures and a mechanism for the formation of these products are proposed.     

Nebenreaktionen bei der radikalischen,intramolekularen Cycloaddition von 2.6-Bis(2-methacryloyloxy-5-methylbenzyl)-4-methylphenylmethacrylat. Beitrag zu einer Matrizenreaktion

Zusammenfassung Die mit 2-Cyano-2-propylradikalen aus AIBN ausgel?ste und beendete intramolekulare Cycloaddition von 2,6-Bis(2-methacryloyloxy-5-methylbenzyl)-4-methylphenylmethacrylat (1) gibt die Cycloaddukte 4-Methyl-1,2,6-benzoltriyl-2,6-bis(4-methyl-2-methy-len-1,2-phenylen)-2,9-dicyano-2,3,5,7,9-pentamethyl-3, 5,7-dekantricarboxylat (1a) und -2,9-dicyano-2,3,5,8,9-pentamethyl-3,5,8-dekantricarboxylat (1b), welche molekulareinheitliche Leiteroligpmere vorstellen. Daneben bildeten sich 10-(2-Cyano-2-methylpropyl)8-(2-cyano-2-propyl)-4- {2-[(2-cyano-2-methylpropyl) acryloyloxy]-5-methylbenzyl∼-2,8,10,15-tetramethyl-7, 11-dioxo-dibenzo[b,e]-1,7-dioxacyclododekan-2,5-dien (1c) und 6 {2-[4-Cyano-2-(2-cyano-2-propyl)-2,4-dimethylvaleryloxy]-5-methylbenzyl}-4,4′-dimethyl-2,2′-methylendiphenyl-bis[2-(2-cyano-2-methylpropyl) acrylat] (1d). Bezogen auf den Ausgangsester1 konnten insgesamt 92% getrennte und dünnschicht-chromatographisch reine Reaktionsprodukte gefa?t werden. Die den Verbindungen zugeordneten Strukturen wurden mittels IR- und UV-Spektren sowie¹H-NMR- und massenspektrometrische Analyse gesichert. Die Cycloaddukte1a und1b sind Produkte einer synthetischen Matrizenreaktion(7), deren Ergebnisse an anderer Stelle mitgeteilt werden soll.

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Summary The intramolecular cycloaddition of 2,6-bis(2-methacryloyloxy-5-methylbenzyl)-4-methylphenyl-methacrylate (1) was started and terminated by 2-cyano-2-propyl radicals from azoisobutyronitrile. The cycloadducts are 4-methyl-1,2,6-benzoltriyl-2,6-bis (4-methyl-2-methylene-1,2-phenylene)-2,9-dicyano-2,3, 5,7,9-pentamethyl-3,5,7-decanetricarboxylate (1a) and-2,9-dicyano-2,3,5,8,9-pentamethyl-3,5,8-decanetricarboxylate (1b), which are also molecularly uniform ladder oligomers. The side products are e]-1,7-dioxacyclododecane-2,5-diene (1c) and 6{2-[4-cyano-2-(2-cyano-2-propyl)-2,4-dimethylvaleryloxy]-5-methylbenzyl∼-4,4′-dimethyl-2,2′-methylenediphenyl-bis[2-(2-cyano-2 methylpropyl)acrylate] (1d). All together and relative to the starting ester1 92 % thin layer chromatographically pure reaction products could be isolated. The suggested structures of the compounds were confirmed by infrared and ultraviolet spectra as well as by¹H-NMR and mass spectroscopical analysis. The cycloadducts1a and1b are compounds of a matrix reaction (7). Their results will be published elsewhere.

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Mit 3 Abbildungen und 5 Tabellen