Synthesis and characterization of functional cyclopentasilanes

Cleavage of the exocyclic Si-Si-bond of phenyldimethysilylnonamethylcyclopentasilane 3 by sodium ethoxide followed by chlorination with acetyl chloride leads to the monofunctional chlorononamethylcyclopentasilane 5 . Subsequent hydration gives hydrononamethylcyclopentasilane 6 , which can be easily converted to the corresponding bromo and iodo derivatives 7 , 8 . Fluorononamethylcyclopentasilane can be prepared upon treatment of 7 with ZnF₂. A different but convenient synthetic pathway to the halononamethylcyclopentasilanes has also been achieved employing the corresponding trifluoromethanesulfonic acid ester 11 . The halogen derivatives—as expected—show a strong influence on the physical properties of the compounds. These functionalized cyclopentasilanes may serve as useful synthetic tools in building larger oligosilane ring systems.     

Spectral properties of organometallic transition metal complexes I–Mass spectra of haloacteophenones haloacetylferroce,Fc?CO–CH2X,and related ferrocence complexes FcCOCI and FcCH2CI

The mass spectral properties of the title compounds have been recorded and compared. For the haloacetyl systems ring expansions to tropylium ions and π-benzene iron ions are observed. A major ion present in all haloacetyl spectra is that derived from the corresponding acetyl compound, CH₃CO-, formed via an instrument catalyzed reduction of the halo compounds by residual water. Some substituent effects are observed. Considerable halogen migration to iron is observed for the ferrocene complexes.     

Synthesis and spectroscopic studies of optically active n‐acetyl butenoates and n‐acetyl‐2‐alkyl‐pyrrolin‐4‐ones

The synthesis of a series of optically active N‐acetyl butenoates 3–5 is described using a facile methodology. These butenoates undergo cyclization to the corresponding N‐acetyl‐2‐alkyl‐pyrrolin‐4‐ones 6,7 retaining their stereochemical integrity. The structure of the newly synthesized compounds has been elucidated through ¹H‐¹³C NMR, IR spectroscopy and their enantiomeric excesses have been measured by chiral HPLC analysis.     

5‐Fluoro‐1‐octanoyl­uracil

The crystal structure of 5‐fluoro‐1‐octanoyl­uracil [5‐fluoro‐1‐octanoyl­pyrimidine‐2,4(1H,3H)‐dione, C₁₂H₁₇FN₂O₃], a lipophilic prodrug of 5‐fluoro­uracil, is described. The 5‐fluoro­pyrimidine‐2,4(1H,3H)‐dione moiety is similar to the known structure of 1‐acetyl‐5‐fluoro­uracil. The 1‐octanoyl group and the 5‐fluoro­uracil moiety are essentially coplanar, with the octanoyl carbonyl group oriented towards the the ring C—H group and away from the nearer ring carbonyl group. The torsion angle C—N—C—O (from the ring CH group to the octanoyl carbonyl group) of 9.2 (2)° is similar to the corresponding torsion angles reported for 1‐acetyl‐5‐fluoro­uracil (17.3 and 1.6°) and 1,3‐di­acetyl‐5‐fluoro­uracil (8.8°).     

Aminolysis of methoxy groups in pyrimidine derivatives. Activation by 5‐nitroso

The nucleophilic substitution of 2‐mefhoxy groups in pyrimidine derivatives was strongly activated by introduction of a 5‐nitroso group on to the pyrimidine ring. The aminolysis of several 2‐methoxy‐5‐nitrosopyrimidine derivatives was performed at room temperature in hydroxylic as well as in non‐hydroxylic media with different primary amines in short time and good yields. The aminolysed substrates include 6‐[(per‐O‐acetyl)glycosyl]aminopyrimidines which afforded the corresponding 2‐aminopyrimidines without harming the acetyl protecting groups of the sugar moiety.     

Synthesis and reactivity of 4-substituted-2,3-dihydrobenzo-1,4-thiazines

A series of derivatives of 4H-2,3-dihydrobenzo-1,4-thiazine has been prepared. 4-Acetyl-2,3-dihydrobenzo-1,4-thiazine undergoes self-condensation by n-butylmagnesium bromide affording the corresponding 4-aceto-acetyl-2,3-dihydrobenzo-1,4-thiazine, which, is converted to 5H-1,4-thiazino[2,3,4-if]quinolin-5-one. Halogena-tion of the acetyl derivative takes place at the position 2 of the heterocyclic ring and oxidation leads to 1-oxides and 1,1-dioxides.     

A new direction in the alkylation of 5‐acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile with active methylene reagents

In this paper, we report a new synthesis route to 4H‐pyran derivatives and a plausible reaction mechanism. The interaction of 5‐acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile with different active methylene reagents gives rise to the cleavage and subsequent recyclization of the pyran ring to afford the corresponding 4H‐pyran derivatives.     

Synthesis and structural characterisation of 4H‐1,3‐benzothiazine derivatives

The ring‐closure reactions of N‐arylthiomethylaroylamide derivatives ( 1a‐g ) in the presence of phospho ‐rus oxychloride gave 2‐aryl‐4H‐1,3‐benzo‐thiazines (2a‐g). 2‐(3‐Chlorophenyl)‐6‐methyl‐4H‐1,3‐benzoth‐iazine ( 2b ) was reduced with Zn to obtain the corresponding 2,3‐dihydro derivative ( 3b ). Potassium permanganate oxidation of 2‐(4‐chlorophenyl)‐2,3‐diethoxy‐4H‐ ( 2e ) and 2‐(2‐fluorophenyl)‐6,7‐diefhoxy‐4H‐1,3‐benzo‐thiazines ( 2g ) gave the corresponding 4‐ones ( 4e,g ). The reactions of 2‐(4‐chlorophenyl)‐6‐mefhyl‐4H‐1,3‐benzofhiazine ( 2c ) with substituted acetyl chlorides led to linearly condensed ß‐lactams ( 5a,b ). The structures of the compounds studied were confirmed by ¹H and ¹³C NMR and by their characteristic mass spectrometric fragmentations.     

Photoswitchable “Turn‐on” Fluorescence Diarylethenes: Substituent Effects on Photochemical Properties and Electrochromism

A series of “turn‐on” fluorescence diarylethenes derived from 2,3‐bis(2‐methylbenzo[b]thiophen‐3‐yl)‐5,6‐dihydro‐4H‐thieno[2,3‐b]thiopyran‐4‐one ( 1 ) with alkyl and acetyl substituents were synthesized. The photochemical and photophysical properties of these derivatives, including the photoreaction of crystalline 1 , were thoroughly investigated to reveal substituent effects on their properties. The results indicated that alkyl substituents did not significantly affect the absorption and emission spectra of the diarylethenes. However, large absorption and emission wavelength shifts were observed for the diarylethene with an acetyl substituent due to extension of π–π conjugation. Significantly, all of the fluorescent ring‐closed forms of the compounds isomerized to their ring‐open forms in the presence of Cu²⁺ in the dark. EPR results provide clear evidence for the formation of the compound 1 radical cation intermediate that might be generated in the reaction between c‐ 1 and Cu²⁺. DFT calculations found that the ground‐state activation energy for ring‐opening of 1^.+ was approximately 9.2 kcal mol^?1 lower than that of 1 without Cu²⁺, such that a Cu²⁺‐catalyzed oxidative cycloreversion reaction at room temperature might be possible.     

Furopyridines. XXII. Elaboration of the C-substituents alpha to the heteronitrogen atom of furo[2,3-b] -, -[3,2-b] -, -[2,3-c]- and -[3,2-c]pyridine

The Grignard reaction of fused ring cyanopyridine derivatives 1a-d with methyl- and phenylmagnesium bromide yielded the corresponding acylpyridine compounds 2a-d and 3a-d . Furopyridine N-oxides 4a-d were converted into the compounds having a phenyl group at the α-position to the ring nitrogen 5a-d . Reduction of 1a-d and the carboxylic esters 6a-d with diisobutylaluminium hydride yielded the corresponding amines 7a-d and aldehydes 9a-d . The aldehydes were converted to nitroethanol derivatives 10a-d by condensation with nitromethane and acrylic ester compounds 11a-d by the Wittig-Horner reaction with methyl diethyl phosphonoacetate.     

A Facile and Efficient Synthesis of Novel 1,2,4-Triazolo[5,1- b ]quinazolin-9-one Derivatives

 A facile and efficient synthesis of a series of novel 1,2,4-triazolo[5,1-b]quinazolines is described. 2,3-Diaryl-2,3-dihydro-1H-1,2,4-triazolo[5,1-b]quinazolin-9-ones were obtained by reaction of 3-amino-2-arylamino-3H-quinazolin-4-ones with aromatic aldehydes as well as by ring closure of the corresponding anils. Treatment of 3-amino-2-arylamino-3H-quinazolin-4-ones with aromatic carboxylic acids afforded 2,3-diaryl-3H-1,2,4-triazolo[5,1-b]quinazolin-9-ones which could also be synthesized by dehydrogenation of the corresponding dihydro derivatives. Reaction of 3-amino-2-arylamino-3H-quinazolin-4-ones with diethyl malonate and acetylacetone gave 3-aryl-3,9-dihydro-9-oxo-1,2,4-triazolo[5,1-b]quinazolin-2-yl-acetic acid ethyl ester and 3-aryl-2-methyl-3H-1,2,4-triazolo[5,1-b]quinazolin-9-ones, respectively. The latter compounds were also prepared via reaction with acetic anhydride, whereas acetylation with acetic anhydride in the presence of pyridine afforded the acetyl derivatives.     

Bridgehead nitrogen heterocycles. VI. The reaction of 1-amino- and 1,2-diaminopyridinium salts with β-dicarbonyl compounds

1,2-Diaminopyridinium iodide underwent reaction with ethyl acetoacetate to form 1,4-dihydro-2-methyl-4-oxopyrido[1,2-a]pyrimidin-1-ium iodide, and with acetyl acetone it gave 2,4-dimethylpyrido[1,2-a]pyrimidin-5-ium iodide. Though 2-acetylcyclohexanone gave the corresponding 5-methyl-1,2,3,4-tetrahydropyrido[1,2-a]quinazolin-11-ium iodide, no reaction was observed with 2,6-dimethyl-3,5-heptanedione, 1-benzoylacetone, 1,3-diphenyl-1,3-propanedione and its p-methoxyphenyl derivative. However, 1-aminopyridinium iodide and acetyl acetone in the presence of base gave 3-acetyl-2-methylpyrazolo[1,5-a]pyridine and 1-amino-2-methylpyridinium iodide yielded the corresponding 3-acetyl-2,7-dimethylpyrazolo[1,5-a]pyridine. With ethyl acetoacetate, the latter salt formed 3-ethoxycarbonyl-2,7-dimethylpyrazolo[1,5-a]pyridine but with 2,6-dimethyl substituents in the pyridine ring no condensation occurred. Reaction of 1-amino-2-methylpyridinium iodide with benzaldehyde gave N-benzalimino-2-methylpyridinium iodide which, on treatment with base, resulted in the formation of 2-picoline and benzonitrile, providing a convenient method of deamination.     

Direct Umpolung of Glycals and Related 2,3‐Unsaturated N‐Acetylneuraminic Acid Derivatives Using Samarium Diiodide

The umpolung of glycals with samarium diiodide offers a simple route to novel carbohydrate‐derived nucleophilic reagents in a single step using a readily available reductant. The corresponding allyl samarium reagent that arises from the hexose series reacts with ketones at the C3 position with high stereoselectivity; carbon–carbon bond formation takes place only anti to the substituent at the C4 position of the dihydropyran ring. For the sialic acid series, the completely regio‐ and stereoselective coupling process of the samarium reagent occurs at the anomeric carbon atom and provides a new approach to the α‐C‐glycosides of N‐acetyl neuraminic acid.     

Reaction of 1,3,4-thiadiazolo and 1,3,4-triazolo[3,2-c]quinazoline derivatives with active methylene compounds

Fused quinazoline derivatives 1 and 4 react with active methylene compounds and depending on the annelated five-membered ring, two types of transformations have been observed. The 1,3,4-thiadiazolo[3,2-c]quinazoline 1 , underwent the five-membered ring opening reaction to afford the 3,4-dihydroquinazolines 2 in good yields, whereas the 1,3,4-triazolo[3,2-c]quinazoline 4 underwent nucleophilic attack at 2-position of the quinazoline ring to yield the corresponding 1,2,4-triazoles 5 .     

A Facile and Efficient Synthesis of Novel 1,2,4-Triazolo[5,1-b]quinazolin-9-one Derivatives

Summary.  A facile and efficient synthesis of a series of novel 1,2,4-triazolo[5,1-b]quinazolines is described. 2,3-Diaryl-2,3-dihydro-1H-1,2,4-triazolo[5,1-b]quinazolin-9-ones were obtained by reaction of 3-amino-2-arylamino-3H-quinazolin-4-ones with aromatic aldehydes as well as by ring closure of the corresponding anils. Treatment of 3-amino-2-arylamino-3H-quinazolin-4-ones with aromatic carboxylic acids afforded 2,3-diaryl-3H-1,2,4-triazolo[5,1-b]quinazolin-9-ones which could also be synthesized by dehydrogenation of the corresponding dihydro derivatives. Reaction of 3-amino-2-arylamino-3H-quinazolin-4-ones with diethyl malonate and acetylacetone gave 3-aryl-3,9-dihydro-9-oxo-1,2,4-triazolo[5,1-b]quinazolin-2-yl-acetic acid ethyl ester and 3-aryl-2-methyl-3H-1,2,4-triazolo[5,1-b]quinazolin-9-ones, respectively. The latter compounds were also prepared via reaction with acetic anhydride, whereas acetylation with acetic anhydride in the presence of pyridine afforded the acetyl derivatives. Received March 22, 2001. Accepted (revised) May 11, 2001     

Ring opening of 2-acylaziridines by acid chlorides

Good nucleophilicity of the ring nitrogen in chiral (2R,1′R)-2-acyl-(1′-phenylethyl)aziridines initiated the reaction with various acid chlorides to form the corresponding acylaziridinium ion intermediates whose rings were opened by the chloride anion to yield the β-amino-α-chlorocarbonyl compounds. The subsequent displacement of the chloride with the internal oxygen nucleophile originated from methylchloroformate, acetyl chloride, and methyl chlorooxoacetate yielded oxazolidin-2-ones, β-amino-α-acetyloxypropionates, and morpholin-2,3-diones, respectively.     

Reactions of 2,3-dihydro-1H-cyclohepta[b]pyrazines with acyl halides

2 When3-dihydro-1H-cyclohepta[b]pyrazine ( 3 ) was treated with acetyl chloride under the Friedel-Crafts conditions, its pyrazine ring opened to afford 2-[N'-acetyl-(2-aminoethyl)amino]tropone. Reactions with propionyl and butyryl chloride also gave similarly ring-opened products. On the other hand, aromatic benzoyl chlorides reacted with compound 3 to afford N-benzoyl-substituted 2,3-dihydro-1H-cyclohepta[b]pyrazines, in addition to ring-opened compounds.     

萘并呋喃类化合物的染料化光氧化及其杂环衍生物的合成与表征

萘并呋喃类化合物1、7在四苯基卟啉存在与氧低温反应给出相应的二氧杂环丁烷类产物2、8，室温下分别全部分解成乙酰基乙酰氧基化合物4、9。2和盐酸作用可给出呋喃3-位甲基及所在萘半环β位的二氯代产物6。4与盐酸反应通过失去萘α位的酰基，形成羟基呋喃化合物3，1在三溴化硼酸解下亦可得同一产物。4在醋酸钠/酸酐中环构生成3-乙酰基吡喃酮(5)。     

3‐Hydrazido and 3‐Hydrazono Derivatives of Tenuazonic Acid and their Herbicide Evaluation

With the aim of optimizing the structure of tenuazonic acid and improving the herbicidal activity, hydrazine moieties were introduced to the 3‐position of pyrrolidine‐2,4‐dione scaffold of tenuazonic acid. 3‐Hydrazido‐pyrrolidine‐2,4‐dione compounds ( 4a , 4b , 4c , 4d , 4e ) were prepared from corresponding carboxylates and hydrazines via a microwave‐assisted amidation, whereas 3‐hydrazono compounds ( 7a , 7b , 7c , 7d , 7e ) were prepared from corresponding 3‐acetyl pyrrolidine‐2,4‐dione. Both of the two structures also exhibited herbicidal activities, especially against the dicotyledonous species amaranth pigweed (Amaranthus retroflexus), but with different structure‐activity relationship.     

Thallium(III) Nitrate Mediated Ring Contraction of 2‐Aryl‐1,2,3,4‐tetrahydro‐4‐quinolones: Stereoselective Synthesis of trans Methyl 2‐Aryl‐2,3‐dihydroindol‐3‐carboxylates

The ring contraction of N‐acetyl‐2‐aryl‐1,2,3,4‐tetrahydro‐4‐quinolones 1a–d with thallium(III) nitrate in trimethyl orthoformate afforded stereoselectively trans methyl N‐acetyl‐2‐aryl‐2,3‐dihydroindol‐3‐carboxylates 5a–d by oxidative rearrangement of aryl ring A.