Benzoxazol-2 (3H)-one and 1,3,4-oxadiazol-2(3H) -one derivatives from substituted enaminones and ketoenamines

Enaminones and ketoenamines bearing a hydrazine type substituent undergo side chain thermal cyclization, the former into benzoxazol-2 (3H)-one derivatives and the latter into 1, 3, 4-oxadiazol-2 (3H)-one derivatives. Factors affecting such reactions are discussed.     

Novel syntheses of 3-cyano-3,4-dihydroquinolin-2(1H)-one and derivatives of 2,3-dicarbomethoxy-2-hydroxycyclopenta[b]quinoline

A facile solid phase conversion of 2-chloro-3-cyano-4-substituted-1,4-dihydroquinolines to 3-cyano-4-substituted-3,4-dihydroquinolin-2(1H)-ones in almost quantitative yields and a novel synthesis of 2,3-dicarbomethoxy-2-hydroxycyclopenta[b]quinoline are described.     

New synthesis of 4,5-dihydro-1,2,4-triazin-3(2H)-one derivatives through cyclic transformation of 1,3,4-oxadiazol-2(3H)-one derivatives

Some 5-aryl(or benzyl)-2-oxo-1,3,4-oxadiazole-3(2H)-acetones or acetophenones 2 were easily prepared. These compounds reacted with hydrazine derivatives to give 4,5-dihydro-1,2,4-triazin-3(2H)-one derivatives 3 , 4 and 6 in good yields. With phenylhydrazine, the intermediate hydrazones 5 were obtained. Their conversion into triazinones necessitated the presence of sodium ethylate.     

One-pot near-ambient temperature syntheses of aryl(difluoroenol) derivatives from trifluoroethanol

Difluoroalkenylzinc reagents prepared from 1-(2'-methoxy-ethoxymethoxy)-2,2,2-trifluoroethane and 1-(N,N-diethylcarbamoyloxy)-2,2,2-trifluoroethane at ice bath temperatures underwent Negishi coupling with a range of aryl halides in a convenient one pot procedure. While significant differences between the enol acetal and carbamate reagents were revealed, the Negishi protocol compared very favourably with alternative coupling procedures in terms of overall yields from trifluoroethanol.     

Electrochemical synthesis of 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives

The 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives have been synthesized by direct electrochemical oxidation of catechols in the presence of 4-mercaptocoumarin as a nucleophile in water/acetonitrile (50/50) solution, in a one-pot process, at carbon rod electrode, in an undivided cell and in constant current conditions, through an EC mechanism. The products are characterized by spectra data. Besides, the difference in electrochemical oxidation of catechol in the presence of 4-hydroxycoumarin and 4-mercaptocoumarin explained by computational structure, natural bond orbital (NBO) analysis and density functional theory (DFT: B3LYP/6-31G*//B3LYP/6-31G*) based methods, using the GAUSSIAN 98 package of programs.     

One-pot syntheses of 2-pyrazoline derivatives

Hydrazinediium dithiocyanate and α,β-unsaturated ketones give in one-pot reactions 1-thiocarbamoyl-2-pyrazolines and 1-formyl-2-pyrazolines. The syntheses of pyridine-2-thiones, pyrimidine-2-thiones and bicyclo[2.2.2]octan-2-ones from ammonium thiocyanates and ketones by analogous procedures are reviewed. The mechanisms of the ring formations are discussed. Crystal structure analyses of a 1-thiocarbamoyl- and a 1-formyl-2-pyrazoline are given.     

1,4-Benzodioxin-2(3H)-one and some of its derivatives

The methods of synthesis of 1,4-benzodioxin-2(3H)-one have been reexamined. Frequently quoted in the literature the method of Ghosh has been found to give impure (2-hydroxyphenoxy)acetic acid rather than the lactone. Using various methods some simple derivatives of the title lactone substituted in the benzene ring have been prepared and characterized. The bromination of the lactone with NBS gives predominantly 7-bromo-1,4-benzodioxin-2(3H)-one under electrophilic conditions, while 6-bromo-1,4-benzodioxin-2(3H)-one is obtained as a major isomer under photolytic conditions.     

Synthesis of pyridin-2(1H)-one derivatives via enamine cyclization

The nucleophilic vinylic substitution reaction of the aliphatic enaminone 3-dimethylamino-2-formyl acrylonitrile 1 with the nucleophiles malononitrile and ethyl cyanoacetate produced the two unusual reaction adducts 3a and 3b in good to moderate yield under milder reaction conditions. Upon reaction with aromatic amines, these adducts yielded enamines 4 and 5, which eventually cyclized in the presence of base to produce the novel pyridin-2(1H)-one derivatives 8 and 9.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Efficient syntheses of 2-chloro-2'-deoxyadenosine (cladribine) from 2'-deoxyguanosine(1)

We report efficient syntheses of the clinical agent cladribine (2-chloro-2'-deoxyadenosine, CldAdo), which is the drug of choice against hairy-cell leukemia and other neoplasms, from 2'-deoxyguanosine. Treatment of 3',5'-di-O-acetyl- or benzoyl-2'-deoxyguanosine (1) with 2,4,6-triisopropyl- or 4-methylbenzenesulfonyl chloride gave high yields of the 6-O-arylsulfonyl derivatives 2 or 2'b. Deoxychlorination at C6 of 1 also proceeded to give the 2-amino-6-chloropurine derivative 5 in excellent yields. The nonaqueous diazotization/chloro dediazoniation (acetyl chloride/benzyltriethylammonium nitrite) of 2, 2'b, and 5 gave the 2-chloropurine derivatives 3, 3'b, and 6, respectively. The selective ammonolysis at C6 (arylsulfonate with 3 or chloride with 6) and accompanying deprotection of the sugar moiety gave CldAdo (64-75% overall yield from 1).     

The syntheses of some novel (naphthalen-1-yl-selenyl)acetic acid derivatives

Some new (naphthalen-1-yl-selenyl)acetic acids derivatives 7a-d have been synthesized by two different methods, using naphthylselenols or naphthylselenocyanates. The structures of the products were investigated by spectroscopic methods.     

Stereospecific syntheses of new manganese(I) isocyanide derivatives

Three series of cationic manganese(I) carbonyls are reported: [Mn(CO)_5-n(CNMe)_n(CNPh)]PF₆ (n = 1 → 4), [Mn(CO)_5-n(CNMe)(CNPh)_n]PF₆ (n = 1 → 4), and [Mn(dpe)(CO)_4-n(CNMe)_n]PF₆ (n = 1 → 4). Most of these compounds were prepared from a substituted metal carbonyl halide by replacement of halide ion by an added ligand (CNR or CO), such reactions requiring an added halide ion acceptor (Ag⁺ or AlCl₃). The added ligand enters the site of departing halide ion. It was possible to prepare isomers of many compounds reported, taking advantage of this stereospecificity. Structures of the products were defined, often unequivocally, by infrared and nmr spectroscopic data. Cyclic voltammetry showed that these compounds undergo one electron oxidations, the ease of oxidation determined by the nature of the ligand groups and the stereochemistry.     

N-Functionalised polyfluoropyridazin-3(2H)-one derivatives

Pyridazin-3(2H)-one systems have very useful biological properties and have found many applications within the pharmaceutical and agrochemical industries but, in general, synthesis of polysubstituted analogues can be very difficult to achieve. An approach to the syntheses of polyfunctional pyridazinone systems involving sequential nucleophilic substitution reactions of N-aryl and N-THP protected 4,5,6-trifluoropyridazin-3(2H)-ones as the core scaffolds is described.     

1,3-Dipolar cycle-addition of 2-diazoalkanes to pyridazin-3(2H)-one derivatives. The formation of 3H-pyrazolo[3,4-d]pyridazin-4(5H)-one and 3H-pyrazolo[3,4-d]pyridazin-7(6H)-one derivatives

1,3-Dipolar cycloadditions of diazoalkanes to pyridazin-3(2H)-ones 1–7 and pyridazin-3(2H)-thiones 8 and 9 are regioselective producing 3H -pyrazolo[3,4-d]pyridazin-4(5H)-ones 15–19, 27–29 and 34–38 as the major products. In some instances, the isomeric 3H-pyrazolo[3,4-d]pyridazin-7(6H)-ones, such as 20 and 23 were isolated as the minor products. From 3 and 6 the primary 3a,7a-dihydro cycloadducts 25 and 26 , and rearranged 1,2-dihydro intermediate 31 were isolated. From 10 and 1-diazoindane the isomeric exo- and endospiro products 39 and 40 were formed.     

Synthesis of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives from curcuminoids

Series of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives were synthesized in acceptable to good yields by treatment of the curcuminoids with aqueous ammonia,the mechanism was proposed.By modification of the primary products,total 13 new compounds were obtained.The structures of all products were elucidated by spectroscopy analysis including HR-MS,~1H NMR and ~(13)C NMR.     

Stereoselective syntheses of pharmaceutically relevant chiral tetrahydrofurans from (S)- and (R)-glyceraldehyde derivatives

A practically simple and flexible method of making chiral tetrahydrofurans of therapeutic relevance is reported from glyceraldehyde derivatives as chiral synthons. One of the stereocentres is derived from glyceraldehyde derivatives, while the other one is introduced by Sharpless asymmetric epoxidation using either (+)- or (−)-DIPT.     

Highly functionalized and stereocontrolled syntheses of 2-(2-methylenecycloalkyl)-furan derivatives by Pd-catalyzed cycloreduction

[structure: see text]. We have discovered a new method employing Pd-catalyzed cycloreduction of conjugated enynals 1 bearing an alkyne unit leading to the corresponding 2-(2-methylenecycloalkyl)-furans 2a-j and a related compound 7 in good to excellent yields.     

Stereodivergent syntheses of anisomycin derivatives from D-tyrosine

[structures: see text] Enantiomerically pure 2-alkyl-3-acetoxy-4-iodopyrrolidines with all groups cis, and all adjacent groups trans (10 and 17), important precursors for the synthesis of pyrrolidinediols, have been prepared from D-tyrosine through regio- and diastereoselective reduction of a vinyl ketone and subsequent iodoamidation controlled by minimization of nonbonding steric interactions. Highly stereodivergent Woodward-Prevost methodology, applied to both iodopyrrolidines, yielded enantiomerically pure (2R,3R,4R)-, (2R,3R,4S)-, and (2R,3S,4R)-deacetylanisomycin (3, 4, and 5), each in excellent de. Incorporation of differential protection of the hydroxyl groups led to a one-pot synthesis of (2R,3R,4R)-anisomycin 2.