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1.
A novel acid-catalyzed ring expansion of methanofullerenes bearing an alpha-ylidic ester has been investigated. Treatment of dialkyl acetylenedicarboxylate and tricycloalkylphosphine with C(60) led to the isolation of a methanofullerene ylide after passing the reaction mixtures through a basic alumina column. If the reaction mixture was passed through a silica gel column, a cyclopentanofullerene was isolated instead. These new cyclopentanofullerenes consisted of a fused cyclopentanone ring bearing an alpha-hydroxy ester and a phosphonium ylide and were confirmed by their NMR, mass, and X-ray diffraction data. The cyclopentanofullerenes were formed by the ring expansion of the corresponding methanofullerenes in the presence of silica gel. The ring expansion also proceeded by treating methanofullerene with acetic acid in chloroform. On the other hand, the methanofullerenes from RO(2)CCCCO(2)R, PAr(3), and C(60) were stable in silica gel. However, upon heating with acetic acid at 50 degrees C, they underwent ring expansion and dephosphination to give cyclopentenofullerenes. An implicit vinyl cyclopropane ring expansion mechanism was proposed to account for this novel acid-catalyzed rearrangement.  相似文献   

2.
Chiral diaminophosphines 4 were prepared from (S)-prolinol-derived aminophosphine oxide 5 by bromination with ring expansion followed by amination with ring contraction and reduction, using trichlorosilane. In the presence of 4 as a ligand, palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate (11) with a dialkyl malonate-BSA-LiOAc system was successfully carried out with good enantioselectivities (up to 98% ee).  相似文献   

3.
An unexpected ring expansion reaction was observed to give the 3-substituted 8,9-didehydroazepinoindolines when 3-substituted pyrroloindolines reacted with electron-deficient acetylenes in the presence of catalytic amount of CuI. The ring expansion reaction proceeded via a three-step one-pot cascade pathway of aza-Michael-addition/ring-opening/iminium-cyclization.  相似文献   

4.
We report a novel approach to prepare five- and six-membered heterocyclic compounds via a ring expansion of monoactivated methylenecyclopropanes (MCPs) with aldimines and aldehydes in the presence of MgI(2). Monoactivated MCPs behave as homo-Michael acceptors to afford bifunctional vinylogous enolates in the presence of MgI(2). The carbonyl moiety of the monoactivated MCP dramatically influences the reaction site in the dienolate with aryl aldimines and aldehydes as well as the size of the ring. Excellent divergent selectivity to five- vs. six-membered heterocycles is observed: alpha-alkylation/5-exo-tet cyclization (Z = NPh(2)) vs. gamma-alkylation/6-exo-trig cyclization (Z = 2-oxazolidone). Analogously, the reaction of the MCP imide with alkyl aldimines demonstrates the same selectivity by varying the size of electrophile or the reaction temperature. In addition, we observe the first example of the formation of the gamma-alkylation adduct in the reaction of a vinylogous imide enolate with a carbonyl compound.  相似文献   

5.
The ring opening of 1,2-(gem-dibromo)cyclopropyl carbohydrates by two different modes leads to either 2-C-(bromomethylene)pyranosides (using base) or 2-bromooxepines (using silver salts), as shown previously by us for a d-glucal-derived cyclopropane. The base-promoted ring opening is extended to encompass additional alcohol, thiol and amine nucleophiles, and diastereoisomeric cyclopropane precursors. Cross-coupling of the 2-C-(bromomethylene)pyranosides leads to extended 2-C-branched pyranosides. Silver-promoted ring expansion of the cyclopropyl carbohydrates in the presence of various alcohols is described. Cross-coupling of the resulting benzyl 2-bromooxepines affords 2-C-substituted oxepines.  相似文献   

6.
Synthesis of (-)-delobanone   总被引:1,自引:0,他引:1  
On irradiation in the presence of Fe(CO)(5) under a CO atmosphere, the alkenyl cyclopropane 2 underwent smooth ring expansion to give the sesquiterpene (-)-delobabone 3. The alkenyl cyclopropane 2 was prepared from the enantiomerically enriched epoxide 1.  相似文献   

7.
In the presence of a cationic Ru catalyst, 1,6-diynes bearing a terminal styryl moiety underwent [2+2+2] cyclization to produce dehydrobiphenylenes fused with a five-membered ring. Although the cycloadducts were unstable toward purification, their one-pot iodine-mediated ring expansion successfully afforded unprecedented bridged ketone products containing a benzo-fused bicyclo[3.2.1] framework.  相似文献   

8.
Based on the Schmidt reaction and an iodolactone ring expansion reaction, two different synthetic routes to substituted 2,3,4,5-tetrahydro-1H-2-benzazepines were developed. The Schmidt reaction on 2,3-dihydro-2H-1-naphthalenone ( 1 ) gave 3 , the product resulting from the alkyl group migration, as the major product instead of the tetrazole 2. This prompted the investigation of the Schmidt reaction on aromatic ketones 8 and 12. The product 9 due to alkyl group migration was the major product of the Schmidt reaction on 2-methyl-3,4-dihydro-2H-1-naphthalenone ( 8 ). The β-keto diester 12 gave a mixture of decarb-oxylated lactams after the Schmidt reaction. In this case, the lactam 13 resulting from the migration of the aromatic ring dominated over the other lactam 14. When lactam 14 was subjected to nitration, a single regioisomer was produced and transformed to the bromo alcohol 19. The other approach was based on the single pot ring expansion of the iodolactone 22 to the lactam 23 in the presence of methanolic ammonia. The iodolactone 22 was readily prepared from 2-allylbenzoic acid.  相似文献   

9.
By application of substoichiometric amounts (50 mol %) of a chiral Lewis acid, the intramolecular [2+2] photocycloaddition of the title compounds was achieved with high enantioselectivity (up to 94 % ee). Upon cleavage of the cyclobutane ring the resulting tricyclic products underwent ring‐expansion reactions under acidic conditions and formed anellated seven‐ or eight‐membered‐ring systems without racemization. The ring expansion could be combined with a diastereoselective reduction (triethylsilane) or allylation (allyltrimethylsilane) upon BF3 catalysis (48–87 % yield).  相似文献   

10.
Treatment of substituted 1,3-dithiolanes and 1,3-oxathiolanes with methyl diazoacetate in the presence of Rh2(OAc)4 effects ring expansion to the corresponding substituted 1,4-dithiane-2-carboxylates and 1,4-oxathiane-3-carboxylates. The sulfur ylides initially generated in these reactions undergo Stevens rearrangement in competition with both [2,3]-C-C-sigmatropic rearrangement and intramolecular fragmentation. In the case of 2-styryl-substituted 1,3-oxathiolane and 1,3-dithiolane, ring expansion on one-, three- and four-carbons subsequently takes place.  相似文献   

11.
In the presence of a cationic Ru catalyst, 1,6‐diynes bearing a terminal styryl moiety underwent [2+2+2] cyclization to produce dehydrobiphenylenes fused with a five‐membered ring. Although the cycloadducts were unstable toward purification, their one‐pot iodine‐mediated ring expansion successfully afforded unprecedented bridged ketone products containing a benzo‐fused bicyclo[3.2.1] framework.  相似文献   

12.
Under aqueous conditions, 4-azidouracil/tetrazolo[1,5-c]pyrimidin-5(6H)-one nucleosides undergo a very efficient photochemical nitrogen elimination and ring expansion to 1,3,5-triazepin-2,4-dione nucleosides whose structure has been confirmed by X-ray crystallography. In contrast, when the photolysis was attempted under anhydrous conditions in the presence of a nucleophile, a ring contraction reaction occurred, affording 2-oxoimidazolone nucleosides. A mechanism to account for the formation of ring expansion and contraction reactions and involving a carbodiimide intermediate is proposed which is reminiscent of the known photochemical behavior of 2-azidopyridines/tetrazolo[1,5-a]pyridines.  相似文献   

13.
A general approach to 6-phenylthio-substituted 2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones based on the ring expansion reaction of 1,2,3,4-tetrahydropyrimidin-2-ones under the action of nucleophiles has been developed. The first step of the synthesis was preparation of N-[(2-benzoyloxy-1-tosyl)ethyl]urea by three-component condensation of 2-benzoyloxyethanal, urea and p-toluenesulfinic acid. Nucleophilic substitution of the tosyl group in the obtained sulfone with sodium enolates of α-phenylthioketones followed by cyclization-dehydration, and debenzoylation gave 4-hydroxymethyl-5-phenylthio-1,2,3,4-tetrahydropyrimidin-2-ones which were transformed into the 4-mesyloxymethyl-derivatives. Treatment of the latter with nucleophilic reagents, such as NaCN, sodium diethyl malonate, PhSNa, MeONa, NaBH(4), sodium succinimide, or potassium phthalimide, afforded the target multi-functionalized diazepinones. The obtained 6-phenylthio-diazepinones and their 6-tosyl-substituted analogues were converted into 3-substituted 1-carbamoyl-1H-pyrroles under acidic conditions as a result of ring contraction. Effective one-pot synthesis of the latter from 4-mesyloxymethyl-pyrimidines was realized using a ring expansion/ring contraction sequence.  相似文献   

14.
Simultaneous electrochemical ring contraction and expansion reactions remain unexplored to date. Herein, the reductive electrosynthesis of heterocycle-fused fulleroids from fullerotetrahydropyridazines and electrophiles in the presence of a trace amount of oxygen has been achieved with concurrent ring contraction and ring expansion. When trifluoroacetic acid and alkyl bromides are employed as electrophiles, heterocycle-fused fulleroids with a 1,1,2,6-configuration are regioselectively formed. In contrast, heterocycle-fused fulleroids with a 1,1,4,6-configuration are regioselectively produced as two separable stereoisomers if phthaloyl chloride is used as the electrophile. The reaction proceeds through multiple steps of electroreduction, heterocycle ring-opening, oxygen oxidation, heterocycle contraction, fullerene cage expansion, and nucleophilic addition. The structures of these fulleroids have been determined by spectroscopic data and single-crystal X-ray diffraction analyses. The observed high regioselectivities have been rationalized by theoretical calculations. Representative fulleroids have been applied in organic solar cells as the third component and exhibit good performance.  相似文献   

15.
Several [1,2,4]triazolobenzothiadiazocin-11-ones 3 were prepared via ring expansion of [1,2,4]triazolo[3,2-b][2,4]benzothiazepin-10(5H)-ones 1 in presence of sodium azide. The reaction intermediate was isolated and characterized as an aryl isocyanate 2b . A possible pathway for formation of novel triazolobenzothiadiazocin-11-one 3 is described.  相似文献   

16.
On treatment with higher diazoalkanes, 2,4,6/3,5-penta-acetoxy-cyclohexanone (penta-O-acetyl-myo-inosose-2 or -scyllo-inosose) afforded by ring expansion all-trans-penta-acetoxy-C-alkyl-cycloheptanones, which by deacylation were converted to hemiacetals. The reactions with diazoalkanes of the penta-acetoxy-inosose in the presence of aluminium chloride and of the free inosose in water solution have also been studied. The structure, the configuration, and, in some cases, the conformation of the new compounds have been established and some of their reactions have been investigated. The mechanisms of formation of the ring expansion products and of the concomitant spiro-epoxides have been discussed.  相似文献   

17.
A straight forward synthesis of the 1,4,2‐benzodithiazine system bearing an ester functionality as potential inducers of systemic acquired resistance in plants was developed utilizing the ring expansion reaction of 1,3‐benzodithioles. The structure of the isomers obtained was established using x‐ray diffraction. The reactivity of the products towards activated alkynes and ring contraction reactions in the presence of base is discussed.  相似文献   

18.
Molecular iodine (10 mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert-butyldimethyl cyanide to afford protected 5-cyano-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a novel C3-C4 bond cleavage of the beta-lactam nucleus.  相似文献   

19.
Asymmetric synthesis of a trichothecane analogue, 4-deoxyverrucarol (2), was carried out through two types of ring expansion reactions. First, synthesis of the racemate of 2 was investigated. Thus, 1-[1-(tert-butyldimethylsiloxy)-ethyl]-1-methoxycarbonyl-2-hexen-4-on e (10), prepared by Diels-Alder reaction, was converted into the cyclopropylidene 15. The cyclobutanone (+/-)-18 was obtained from 15 via dihydroxylation, followed by successive treatments with SO(2)Cl(2) in the presence of imidazole and Florisil. After transformation of (+/-)-18 into the vinylcyclobutanol (+/-)-19, the second ring expansion reaction was performed with Pd(OAc)(2) to provide the cyclopentanone (+/-)-20. The product was converted into the racemate of 4-deoxyverrucarol (2) through the cyclohexenone (+/-)-22, but the diastereoselectivity during the introduction of the double bond was unsatisfactory. The selectivity was improved in the case of the asymmetric synthesis. The optically active cyclobutanone (+)-18 was prepared via AD reaction of 15 with 73% ee. After the transformation of (+)-18 into the cyclohexanone (-)-30 through the palladium-mediated ring expansion reaction, (-)-30 was subjected to the diastereoselective deprotonation reaction using the chiral amide. The key synthetic intermediate (-)-25 of 4-deoxyverrucarol (2) was synthesized in an optically pure form by taking advantage of a kind of kinetic resolution that occurred during the deprotonation step.  相似文献   

20.
The 4‐hydroxypyridones 7 and 3‐hydroxypyridones 8/9 (azagrevellins) were prepared by reaction of the pyrrolidinetrione 4 and diazoalkanes. The ring enlargement proceeded by anionotropic [1,2]‐rearrangement introducing carbon between C‐3 and C‐4 or, to a lesser extent, between C‐2 and C‐3 due to the different migration aptitudes of the two acyl groups involved. In a cognate manner ring expansion between C‐2 and C‐3 occured by the interaction of diazomethane and the pyrrolidinetrione hydrazone 15 , to give the spiroe‐poxide 16 as the final product. From the reaction of trione 4 and diazomethane, however, the diepoxide 14 was obtained. In this case ring homologation must have taken place by insertion of carbon between C‐4 and C‐5. In a two step ring expansion the pyridones 21 and 22 were obtained from the maleineimides 17.  相似文献   

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