Sharif Digital Repository

Allyl, crotyl, methallyl and cinamyl ethers of 4-hydroxy-, 7-hydroxy-, and 4-methyl-7-hydroxycoumarins have been efficiently synthesized and rearranged to substituted allylcoumarins under microwave irradiation. Irradiation of allylcoumarins in the presence of BF3/ether directly produced substituted dihydrofurocoumarins in good yields  

A new and efficient method has been developed for the synthesis of 5,7-diaryl-5,6,7,8-tetrahydropyrimido[4,5-d]pyrimidine-2,4-dione derivatives by cyclization of 6-aminouracils with N,N′-bis(arylmethylidene)arylmethanes (diimines). The products were formed in good yields and with very good anti-diastereoselectivity. The best yields were obtained when p-toluenesulfonic acid (PTSA) was used as the catalyst. The solvent also played an important role in the optimization. An amino-substituted 6-aminouracil and a corresponding sulfur analog could be successfully employed. In addition, various diimines, electron rich and neutral, could be successfully employed. The products are of relevance as... 

An efficient one-pot synthesis of functionalized trisubstituted thiophenes via the reaction of 3-morpholino-3-thioxopropanenitrile, cyclohexyl isocyanide and -haloketones is reported. This method provides a straightforward route to a variety of highly substituted thiophenes not easily accessible by conventional methods  

The cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[7.3.1.0 2,7]trideca-2(7),11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicar-bonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product  

A theoretical study of the kinetics and mechanism of the cyclization of citronellal in the gas phase was performed using density functional theory methods at the B3LYP level of theory with 6-311G, 6-311G*, 6-31G**, 6-311G**, 6-311 þ G and 6-311 þ þ G basis sets at 298.15 K, 433.15 K, and 473.15 K. Equilibrium molecular geometries and harmonic vibrational frequencies of the reactant, transition state and products were calculated. Rate constants and activation thermodynamic parameters were calculated and showed a fairly good agreement with experimental results. The effect of solvent polarity on the reaction was studied. These calculations indicated that the reaction proceeds through an... 

We report a simple, fast, efficient and benign procedure for solvent-free microwave-assisted one-pot synthesis of symmetrical 4H-pyran-4-ones in the presence of polyphosphoric acid or diphosphorous pentoxide. Various 4H-pyran-4-ones were prepared using this very simple and fast green protocol. ©2007 Sociedade Brasileira de Química  

Gold-catalyzed cyclization of 1,5-diynes with ketones as reagents and solvent provides diversely substituted vinyl ethers under mild conditions. The regioselectivity of such gold-catalyzed cyclizations is usually controlled by the scaffold of the diyne. Herein, we report the first solvent-controlled switching of regioselectivity from a 6-endo-dig- to 5-endo-dig-cyclization in these transformations, providing fulvene derivatives. With respect to the functional-group tolerance, aryl fluorides, chlorides, bromides, and ethers are tolerated. Furthermore, the mechanism and selectivity are put to scrutiny by experimental studies and a thermodynamic analysis of the product. Additionally,... 

The synthesis of a series of benzoxazocines has been achieved in good yields by tandem C-alkylation and intramolecular O-alkylation of 1,3-dicarbonyl compounds with quinolinium salts. This is a novel example of the synthesis of eight-membered rings via a tandem process, which provides a method for the synthesis of medium-ring heterocycles  

Indole-2(3H)thiones were cyclized under the action of 2-fluorobenzoyl chlorides to give thiochromeno[2,3-b]indol-11(6H)-ones or under the action of 2-chloronicotinoyl chlorides to give pyrido[3′,2′:5,6]thiopyrano[2, 3-b]indol-5(10H)-ones. The reaction of cyclization proceeds regioselectively in DMF and does not require transition metals for completion. Obtained heterocycles are isosteric analogues of various tetracyclic indole derived alkaloids  

The reaction of oxiranes with carbon disulfide for preparation of cyclic dithiocarbonates was carried out in water under catalytic amount of an organic base such as dimethylaminopyridine or triethylamine. The reaction conditions are simple and give high yields of desired products.© 2009 HeteroCorporation  

A novel and efficient multicomponent reaction for the synthesis of polysubstituted pyrrolidine derivatives is described under catalyst-free conditions using ultrasonic irradiation. The reactions were performed via a one-pot four-component condensation of secondary amines, carbon disulfide, isocyanides, and gem-dicyano olefins at room temperature to afford polysubstituted pyrrolidines diastereoselectively in 56-96% yields. This is the first report of a Mumm-type rearrangement with dithiocarbamates followed by intramolecular cyclization, which leads to the preparation of the key structure of pyrrolidine. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche... 

(A) Chakraborty and co-workers have developed a green method for the bulk ring-opening polymerization of lactides in the presence of Cu(OAc)2 as a good catalyst to synthesize polymers with different end-terminal groups.3 These polymerizations are highly controlled leading to the formation of polymers with the expected number of average molecular weights and narrow molecular weight distribution. (B) Garden and co-workers have found that the oxidative addition of anilines with 1,4-naphthoquinone to give N-aryl-2-amino-1,4-naphthoquinones can be performed in the presence of catalytic amounts of copper(II) acetate.4 All the reactions are generally more efficient in that they are cleaner, higher... 

An efficient 12-step route for the synthesis of the diterpenoid quinone (±)-danshexinkun A in 23% overall yield from the corresponding highly substituted stilbene using a photocyclization strategy is described  

N-benzyl-DABCO tribromide, a stable, crystalline organic ammonium tribromide (OATB), have been used as an alternative electrophilic bromine source for the efficient oxidative cyclization of thiobenzanilides to the corresponding benzothiazoles under mild conditions. © Georg Thieme Verlag Stuttgart  

Herein, functionalized spiro[indoline-3,5′-pyrazolo[1,2-a]pyridazine]-7′-carbonitrile containing two contiguous chiral stereocenters was efficiently synthesized in a satisfactory yield (up to 91% yield) and with excellent diastereoselectivity. We have reached this satisfactory yield by DABCO-catalyzed [3+3] annulation reactions of an isatin N,N′-cyclic azomethine imine 1,3-dipole with a Knoevenagel intermediate in dichloromethane (DCM) as solvent at ambient temperature; this was an entirely new strategy for creating one quaternary stereogenic center at the position-3 of an oxindole structure using an abnormal tandem Michael addition, N-cyclization, and a unique approach via the azomethine... 

Herein, functionalized spiro[indoline-3,5′-pyrazolo[1,2-a]pyridazine]-7′-carbonitrile containing two contiguous chiral stereocenters was efficiently synthesized in a satisfactory yield (up to 91% yield) and with excellent diastereoselectivity. We have reached this satisfactory yield by DABCO-catalyzed [3+3] annulation reactions of an isatin N,N′-cyclic azomethine imine 1,3-dipole with a Knoevenagel intermediate in dichloromethane (DCM) as solvent at ambient temperature; this was an entirely new strategy for creating one quaternary stereogenic center at the position-3 of an oxindole structure using an abnormal tandem Michael addition, N-cyclization, and a unique approach via the azomethine...