Reaction of sulfene with heterocyclic N,N-disubstituted α-aminomethyleneketones. IX. Synthesis of 1,2-oxathiino[6,5-e]indole derivatives

The polar 1,4-cycloaddition of sulfene to N,N-disubstituted 5-aminomethylene-1,5,6,7-tetrahydro-1-methylindol-4-ones occurred only in the case of aliphatic N-substitution to give, generally in good yield, 4-dialkylamino-3,4,5,6-tetrahydro-7-methyl-7H-1,2-oxathiino[6,5-e]indole 2,2-dioxides IV. Full aromatization of IVa (4-NR₂ = dimethylamino) with DDQ in refluxing benzene gave in low yield 7-methyl-7H-1,2-oxathiino-[6,5-e]indole 2,2-dioxide, whereas the same reaction of IVe (4-NR₂ = morpholinyl) with excess DDQ afforded in low yield 7-methyl-4-morpholinyl-7H-1,2-oxathiino[6,5-e]indole 2,2-dioxide.     

Computational studies of the optical emission of silicon nanocrystals

We have computed absorption and emission energies of silicon nanocrystals as a function of size and of surface passivants, using both density functional theory and quantum Monte Carlo calculations. We have found that the ionic rearrangements and electronic relaxations occurring upon absorption and emission are extremely sensitive to surface chemistry. In particular, nanoclusters with similar sizes and similar absorption gaps can exhibit strikingly different emission energies. Our results provide a unifying interpretation of several recent measurements, which have observed significantly different emission energies from clusters with similar sizes. Our calculations also show that a combination of absorption and emission measurements can provide a powerful tool for identifying both the size and the surface passivants of semiconductor nanocrystals.     

The acylation of an acyl complex resulting in a labile OCO tridentate ligand

The reaction of propionic anhydride with [fac-Ru(C(O)Et)-(CO)2(H2O)3][CF3SO3] produces a new propylidin dipropionato group, which behaves as a tridentate ligand giving the neutral complex Ru(CEt(OC(O)Et)2)(CO)2(CF3SO3).     

Reaction of 2-dimethylaminomethylene-1,3-diones with Dinucleophiles. IV. Synthesis of 5,7-dihydrothiopyrano[3,4-c]pyrazol-4(1H)-ones, 5H-Thiopyrano[4,3-d]isoxazol-4(7H)-one and 6H-Thiopyrano[3,4-d]pyrimidin-5(8H)-ones

The reaction of 2H-thiopyran-3,5(4H,6H)-dione with N,N-dimethylformamide dimethyl acetal gave in good yield 4-dimethylaminomethylene-2H-thiopyran-3,5(4H,6H)dione (II), which afforded 1-substituted 5,7-dihydrothiopyrano[3,4-c]pyrazol-4(1H)-ones with aliphatic and aromatic hydrazines, 5H-thiopyrano[4,3-d]isoxazol-4(7H)-one (IV) with hydroxylamine hydrochloride and 2-substituted 6H-thiopyrano[3,4-d]pyrimidin-5(8H)-ones with amidines and guanidines, generally in satisfactory yields. 4-(t-Butylhydrazonoformyl)-2H-thiopyran-3,5(4H,6H)-dione was isolated as an intermediate in the reaction of II with t-butylhydrazine, whereas formamidine gave with II 4-iminoformyl-2H-thiopyran-3,5(4H,6H)-dione as the sole product. The isoxazole IV isomerized easily with sodium methoxide to 3,4,5,6-tetrahydro-5,5-dihydroxy-3-oxo-2H-thiopyrano-4-carbonitrile.     

New pyrazolo[3,4-b]pyridones as selective A(1) adenosine receptor antagonists: synthesis, biological evaluation and molecular modelling studies

A series of ethyl 4-amino-1-(2-chloro-2-phenylethyl)-6-oxo-6,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carboxylates () has been synthesized as potential A(1) adenosine receptor (A(1) AR) ligands. Binding affinities of the new compounds were determined for adenosine A(1), A(2A) and A(3) receptors. Compounds and showed good affinity (K(i)= 299 nM and 517 nM, respectively) and selectivity towards A(1) AR, whereas showed good affinity for A(2A) AR (K(i)= 290 nM), higher than towards A(1) AR (K(i)= 1000 nM). The only arylamino derivative of the series displayed high affinity (K(i)= 4.6 nM) and selectivity for A(3) AR. Molecular modelling and 3D-QSAR (CoMFA) studies carried out on the most active compounds gave further support to the pharmacological results.     

In silico strategies to describe the formation of the inclusion complex between β-cyclodextrin and β-naphtyloxyacetic acid: a preliminary step towards prediction of log K

Ligand/cyclodextrin is a peculiar type of ligand/receptor system. We report the results of a docking procedure using β-naphtyloxyacetic acid as ligand and various models of β-cyclodextrin as receptor. The results indicate that docking strategies can successfully be applied to any ligand/cyclodextrin system with the final aim of predicting log K values.     

Reaction of ketenes with N,N-disubstituted α-aminomethyleneketones. XI. Synthesis of 2H-pyrano[3,2-g]benzothiazole derivatives

Cycloaddition of dichloroketene to N,N-disubstituted 6-aminomethylene-5,6-dihydro-2-phenylbenzothiazol-7-(4H)ones gave in good yield N,N-disubstituted 4-amino-3,3-dichloro-3,4,5,6-tetrahydro-8-phenyl-2H-pyrano[3,2-g]benzothiazol-2-ones II, which are derivatives of the new heterocyclic system 2H-pyrano[3,2-g]benzothiazole. Dehydrochlorination with triethylamine of II afforded N,N-disubstituted 4-amino-3-chloro-5,6-dihydro-8-phenyl-2H-pyrano[3,2-g]benzothiazol-2-ones III in good to moderate yield. The dimethylamino adduct was dehydrochlorinated in high yield by refluxing in toluene, whereas the diisopropylamino adduct gave in low yield 6-(2,2-dichloroethylidene)-5,6-dihydro-2-phenylbenzothiazol-7-(4H)one with the triethylamine treatment. The dehydrochlorinated product IIId (NR₂ = pyrrolidino) was obtained directly in low yield by cycloaddition of dichloroketene to the corresponding enaminone. Full aromatisation of IIIa,g [NR₂ = N(CH₃)₂ and N(CH₃)C₆H₅, respectively] to the corresponding N,N-disubstituted 4-amino-3-chloro-8-phenyl-2H-pyrano-[3,2-g]benzothiazol-2-ones was accomplished with DDQ in refluxing benzene.     

Reaction of 2-dimethylaminomethylene-1,3-diones with dinucleophiles. X. synthesis of 5-substituted ethyl or methyl 4-isoxazolecarboxylates and methyl 4-(2,2-dimethyl-1-oxopropyl)-5-isoxazolecarboxylate

Reaction of ethyl or methyl 2-dimethylaminomethylene-3-oxoalkanoates with hydroxylamine hydrochloride in methanol solution afforded in high yields the relative esters of 5-substituted 4-isoxazolecarboxylic acids II . These esters were hydrolyzed generally with concentrated hydrochloric acid-acetic acid mixtures to the corresponding carboxylic acids in satisfactory yields. Ethyl or methyl esters II isomerized with sodium ethoxide or methoxide, respectively, to the corresponding esters or hemiesters of 2-cyano-3-oxoalkanoic acids generally in excellent to satisfactory yields. Reaction of methyl 5,5-dimethyl-3-dimethylaminomethylene-2,4-dioxohexanoate with hydroxylamine hydrochloride afforded in moderate yield methyl 4-(2,2-dimethyl-1-oxopropyl)-5-isoxazolecarboxylate, which was converted by acid hydrolysis as above to 4-t-butyl-4-hydroxyfuro[3,4-d]isoxazol-6-(4H)-one.     

Reaction of ketenes with N,N-disubstituted à-aminomethyleneketones. IX. Synthesis of 2H,5H-pyrano[3,2-c][1]benzopyran derivatives

Cycloaddition of dichloroketene to N,N-disubstituted 3-aminomethylene-4-chromanones gave in good yield N,N-disubstituted 4-amino-3,3-dichloro-3,4-dihydro-5H-pyrano[3,2-c][1]benzopyran-2-ones only in the case of aromatic N-substitution. Dehydrochlorination with triethylamine of these adducts afforded N,N-disubstituted 4-amino-3-chloro-5H-pyrano[3,2-c][1]benzopyran-2-ones in good to moderate yield. The cycloaddition to 3-dimethylaminomethylene-4-chromanone led directly to 3-chloro-4-dimethylamino-5H-pyrano[3,2-c][1]benzopyran-2-one.