Stereochemistry of [4 + 2] Cycloadditions of Perfluorinated Selenocarbonyls to 1, 3‐Dienes

In completely stereospecific [4+2] cycloadditions, the perfluorinated selenocarbonyls 1 and 2 react both with trans‐trans‐2, 4‐hexadiene and cis‐trans‐2, 4‐hexadiene to yield 3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2H‐selenapyrans 3 , 4a and 4b . The observed stereoselectivity leads to the conclusion, that the [4+2] cycloaddition of perfluorinated selenocarbonyls follows a concerted pathway. An identical mixture of isomers was isolated when using the precursor for 2 , trimethylstannyl (pentafluoroethyl)selane, which reacts with both 1, 3‐dienes over several weeks to form a mixture of syn‐2‐fluoro‐3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2‐trifluoromethyl‐2H‐selenapyran ( 4a ) and anti‐2‐fluoro‐3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2‐trifluoromethyl‐2H‐selenapyran ( 4b ) in the same ratio as found for 2 , thus proving the intermediate formation of Se=C(F)CF₃ ( 2 ). Complex 2D NMR experiments were used to distinguish the isomers 4a and 4b and to assign the ¹H, ¹³C and ¹⁹F NMR data of the selenaheterocycles.     

A new approach to the synthesis of pyridazino[4,5-c]pyridazinones

The reaction of 5-hydrazinopyridazin-3(2H)-ones 1 with α-keto diester 2 in acetic acid afforded the corresponding 4,6-dihydropyridazino[4,5-c]pyridazin-5(1H)-ones 3 and pyrrolo[2,3-d)pyridazin-4(5H)-ones 4 . Compounds 3 were also obtained from 4-bromo-5-hydrazinopyridazin-3(2H)-ones 8 and 2 under milder conditions. 5-Bromo-4-hydrazinopyridazin-3(2H)-one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7-dihydropyridazino[4,5-c]pyridazin-8(1H)-one 10b , the regioisomer of 3b .     

Facile addition of methyl lithium to a 4-vinylpyridine system

The rapid addition of methyl lithium to the 4-vinylpyridine system present in 4-{2,6-dihydroxy-4-(3-methyl-2-octyl)phenyl}-2-methyl-4-(4-pyridyl)but-3-en-2-ol ( 2 ) is reported. The α and β-4-{2,6-dihydroxy-4-(3-methyl-2-octyl)phenyl}-2,3-dimethyl-4-(4-pyridyl)butan-2-ols 4 and 5 formed, are cyclised by heating with 5N hydrochloric acid to trans and cis-3,4-dihydro-5-hydroxy-7-(3-methyl-2-octyl)-4-(4-pyridyl)-2,2,3-trimethyl-2H-1-benzopyran 6 and 7 respectively.     

The synthesis of 3-deazapyrimidine nucleosides related to uridine and cytidine and their derivatives

Condensation of 2,4-bis(trimethylsilyloxy)pyridine ( 1 ) with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide ( 2 ) gave 4-hydroxy-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-2-pyridone ( 3 ). Deblocking of 3 gave 4-hydroxy-1-β-D-ribofuranosyl-2-pyridone (3′-deazauridine) ( 4 ). Treatment of 4 with acetone and acid gave 2′,3′-O-isopropylidene-3-deazauridine ( 6 ). Reaction of 4 with diphenylcarbonate gave 2-hydroxy-1-β-D-arabinofuranosyl-4-pyridone-O₂←2′-cyclonucleoside ( 7 ) which established the point of gylcosidation and configuration of 4 . Base-catalyzed hydrolysis of 7 gave 4-hydroxy-1-β-D-arabinofuranosyl-2-pyridone (3-deazauracil arabinoside) ( 12 ). Fusion of 1 with 3,5-di-O-p-toluyl-2-deoxy-D-erythro-pentofuranosyl chloride ( 5 ) gave the blocked anomeric deoxynucleosides 8 and 10 which were saponified to give 4-hydroxy-1-(2-deoxy-β-D-erythro-pentofuranosyl)-2-pyridone (2′-deoxy-3-deazauridine) ( 11 ) and its α anomer ( 9 ). Condensation of 4-acetamido-2-methoxypridine ( 13 ) with 2 gave 4-acetamido-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-2-pyridone ( 14 ) which was treated with alcoholic ammonia to yield 4-acetamido-1-β-D-ribofuranosyl-2-pyridone ( 15 ) or with methanolic sodium methoxide to yield 4-amino-1-β-D-ribofuranosyl-2-pyridone (3-deazacytidine) ( 16 ). Condensation of 13 and 2,3,5-tri-O-benzyl-D-arabinofuranosyl chloride ( 17 ) gave the blocked nucleoside 22 which was treated with base and then hydrogenolyzed to give 4-amino-1-β-D-arabinofuranosyl-2-pyridone (3-deazacytosine arabinoside) ( 23 ). Fusion of 13 with 5 gave the blocked anomeric deoxynucleosides 18 and 20 which were deblocked with methanolic sodium methoxide to yield 4-amino-1-(2-deoxy-β-D-erythro-pentofuranosyl)-2-pyridone (2′-deoxy-3-deazacytidine) ( 21 ) and its a anomer 19 . The 2′-deoxy-erythro-pentofuranosides of both 3-deazauracil and 3-deazacytosine failed to obey Hudson's isorotation rule but did follow the “quartet”-“triplet” anomeric proton splitting pattern in the ¹H nmr spectra.     

2-Vinylcyclobutanones by Cycloaddition of Vinylketenes to Simple Olefins

Selected [2+2]-cycloadditions of three alkylvinylketenes 2 to one mono- and seven dialkyl-olefins 3 yielded eleven 2-alkyl-2-vinylcyclobutanones 4 (Tables 1 and 2). Three methods were compared, all involving in situ generation of the ketenes 2 by HCl-elimination from α,β-unsaturated acid chlorides 1 ; the most effective employed a large excess of olefin 3 and a high reaction temperature. The [2+2]-cycloadditions were fully regio- and stereoselective with respect to the olefin 3 , but less so with respect to the ketene 2 , so that - where possible - two stereoisomers of 4 resulted, namely A and B , whose configurations were determined from their ¹H-NMR, spectra, mechanistic considerations and, in one case, 4f , by chemical correlation with a previously known cycloadduct 8 .     

Pyridine nucleosides related to 5-fluorocytosine

4-Amino-5-fluoro-2-pyridone ( 4 ) [5-fluoro-3-deazacytosine] was isolated as the hydrochloride salt from the dealkylation of 4-amino-5-fluoro-2-methoxypyridine ( 2 ), which was obtained from the reduction of 5-fluoro-2-methoxy-4-nitropyridine-N-oxide ( 1 ). Acetylation of 2 gave 4-acetamido-5-fluoro-2-methoxypyridine ( 3 ), which was condensed with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide to give the blocked nucleoside ( 8 ). Removal of the protecting groups gave 5-fluoro-3-deazacytidine. Fusion of the trimethylsilyl derivative of 4 (10), with 2-deoxy-3,5-di-O-p-toluoyl-D-erythro pentofuranosyl chloride gave a mixture of the β and α-anomers 12 and 13 , which were separated and deblocked to yield 5-fluoro-2′-deoxy-3-deazacytidine ( 14 ) and its α-anomer ( 15 ). Several alkylated and acetylated derivatives of 2 were prepared as model compounds for use in the proof of structure.     

Stereocontrol of the Schiff Base of Substituted Benzaldehyde to Staudinger Cycloaddition Reaction

Syntheses of 4 novel chiral azetidin-2-one derivatives,which were characterized by ^1H NMR,IR,specific rotation and elemental analysis,through Staudinger cycloaddition reaction of Schiff base of benzaldehyde with chlorine substitution at different position in benzene ring,were described.For the first time,this type of 3S,4R configuration azetidin-2-one monocrystals with many chiral centers [(3S,4R)-3-hydroxy-N-[(S)-(1-phenyl)ethyl]-4-(2‘‘-chlorophenyl)-azetidin-2-one monocrystal]were obtained,the structures of which were determined by X-ray diffraction analysis.The effects of Schiff base of benzaldehyde with chlorine substitution at different position in benzene ring on stereoselectivity of Staudinger cycloaddition reaction products were discussed and the results are showed as below:2-chlorophenyl Schiff base favored to yield 3S,4R configuration product,but 4-chlorophenyl Schiff base favored to yield 3R,4S configuration product.The reaction orientation of 2,4-dichlorophenyl Schiff base was determined by corporate effect of 2- and 4-chlorine,and that of the 4-chlorine was more obvious.In contrast to 4-chlorophenyl,although the main product was 3R,4S configuration,3-chlorophenyl owned lower selectivity.     

Synthesis of certain exocyclic thiazole nucleosides related to tiazofurin. Formation of a unique acycloaminonucleoside

Several thiazole nucleosides structurally related to tiazofurin (1) and ARPP (2) were prepared, in order to determine whether these nucleosides had enhanced antitumor/antiviral activities. Ring closure of 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)thiourea (4) with ethyl bromopyruvate (5a) gave ethyl 2-(2,3,5-tri-O-benzoyl-β-D-ribofuranosylamino)thiazole-4-carboxylate (6a) . Treatment of 6a with sodium methoxide furnished methyl 2-(β-D-ribopyranosylamino)thiazole-4-carboxylate (9) . Ammonolysis of the corresponding methyl ester of 6a gave a unique acycloaminonucleoside 2-[(1R, 2R, 3R, 4R)(1-benzamido-2,3,4,5-tetrahydroxypentane)amino]-thiazole-4-carboxamide (7a) . Direct glycosylation of the sodium salt of ethyl 2-mercaptothiazole-4-carboxylate (12) with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide (11) gave the protected nucleoside 10 , which on ammonolysis provided 2-(β-D-ribofuranosylthio)thiazole-4-carboxamide (3b) . Similar glycosylation of 12 with 2-deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranosyl chloride (13) , followed by ammonolysis gave 2-(2-deoxy-β-D-ribofuranosylthio)thiazole-4-carboxamide (3c) . The structural assignments of 3b, 7a , and 9 were made by single-crystal X-ray analysis and their hydrogen bonding characteristics have been studied. These compounds are devoid of any significant antiviral/antitumor activity in vitro.     

A Facile Route to Quinazolin-4(3H)-ones Functionalised at the 2-Position

Treatment of 2-methoxyacetamidobenzonitriles or 2-chloroacetamidobenzonitrile with UHP and K₂CO₃ provides a convenient route to 2-methoxymethyl-or 2-chloromethylquinazolin-4(3H)-ones. In addition, demethylation of 2-methoxymethylquinazolin-4(3H)-ones with 48% HBr gives 2-hydroxymethylquinazolin-4(3H)-ones.     

Synthesis of 2′-deoxyribofuranosyl indole nucleosides related to the antibiotics SF-2140 and neosidomycin

The 2′-deoxyribofuranose analog of the naturally occurring antibiotics SF-2140 and neosidomycin were prepared by the direct glycosylation of the sodium salts of the appropriate indole derivatives, with 1-chloro-2- deoxy-3,5-di-O-p-toluoyl-α-D-erythropentofuranose ( 5 ). Thus, treatment of the sodium salt of 4-methoxy-1H- indol-3-ylacetonitrile ( 4a ) with 5 provided the blocked nucleoside, 4-methoxy-1-(2-deoxy-3,5-di-O-p-toluoyl-β- D-erythropentofuranosyl)-1H-indol-3-ylacetonitrile ( 6a ), which was treated with sodium methoxide to yield the SF-2140 analog, 4-methoxy-1-(2-deoxy-β-D-erythropentofuranosyl)-1H-indol-3- ylacetonitrile ( 7a ). The neosidomycin analog ( 8 ) was prepared by treatment of the sodium salt of 1H-indol-3-ylacetonitrile ( 4b ) with 5 to obtain the blocked intermediate 1-(2-deoxy-3,5-di-O-p-toluoyl-β-D-erythropentofuranosyl) ?1H-indol-3-ylace-tonitrile ( 6b ) followed by sodium methoxide treatment to give 1-(2-deoxy-β-D-erythropentofuranosyl)-1H- indol-3-ylacetonitrile ( 7b ) and finally conversion of the nitrile function of 7b to provide 1-(2-deoxy-β-D- erythropentofuranosyl)-1H-indol-3-ylacetamide ( 8 ). In a similar manner, indole ( 9a ) and several other substituted indoles including 1H-indole-4-carbonitrile ( 9b ), 4-nitro-1H-indole ( 9c ), 4-chloro-1H-indole-2-carboxamide ( 9d ) and 4-chloro-1H-indole-2-carbonitrile ( 9e ) were each glycosylated and deprotected to provide 1-(2-deoxy-β-D-erythropentofuranosyl)-1H-indole ( 11a ), 1-(2-deoxy-β-D-erythropentofuranosyl)-1H-indole-4- carbonitrile ( 11b ), 4-nitro-1-(2-deoxy-β-D-erythropentofuranosyl)-1H-indole ( 11c ), 4-chloro-1-(2-deoxy-β-D- erythropentofuranosyl)-1H-indole-2-carboxamide ( 11d ) and 4-chloro-1-(2-deoxy-β-D-erythropentofuranosyl)- 1H-indole-2-carbonitrile ( 11e ), respectively. The 2′-deoxyadenosine analog in the indole ring system was prepared for the first time by reduction of the nitro group of 11c using palladium on carbon thus providing 4-amino-1-(2-deoxy-β-D-erythropentofuranosyl)- 1H-indole ( 16 , 1,3,7-trideaza-2′-deoxyadenosine).     

General preparative route to benzo[g]quinolines (1-azaanthracenes)

A convenient synthetic pathway to benzo[g]quinolines (1-azaanthracenes) has been developed. The nickel catalyzed coupling of methyl 2-chloronicotinate ( 3a ) with benzylic organo zinc reagents 2a-e led to the methyl 2-benzylic substituted nicotinates 4a-e. Treatment of methyl 2-chloro-6-methylnicotinate ( 3b )with 2a in a similar manner led to methyl 2-benzyl-6-methyInicotinate ( 4f ). The coupling of 2-chloro-3-acetylpyridine ( 5 ) with benzyl zinc bromide ( 2a ) led to 2-benzyl-3-acetylpyridine ( 4g ). The coupling of the 2,5-dichlorobenzylic organic zinc reagent ( 2f ) with methyl 2-choronicotinate ( 3a ) was unselective but readily coupled with methyl 2-bromonicotinate ( 6 ) to yield methyl 2-(2,5-dichlorobenzyl)nicotinate ( 4h ). The esters 4a-f,h on reduction with lithium aluminum hydride led to the corresponding alcohols 7a-f,h which were subsequently oxidized with manganese dioxide to the respective 2-benzylic substituted pyridine-3-carboxaldehydes 8a-f,h. In one case the coupling of benzy] zinc bromide ( 2a ) with 2-chloropyridine-3-carboxaldehyde ( 9 ) led directly to 2-benzylpyridine-3-carboxaldehyde ( 8a ), but in poor yield. Cyclizations of the aldehydes 8a-d,f,h or the ketone 4g with polyphosphoric acid afforded the benzo[g]quinolines 10a-d,f-h in high yields. Aldehyde 8e was cyclized to 10e using a solution of sulfuric acid in methanol. Several of the benzo[g]quinolines 10c,d could be readly converted into the benzo[q]quinoline-5,10-diones 11c,d on treatment with ammonium ceric nitrate.     

Instructions to Authors (1994)

(1S,2R,6R,7R)-4-Phenyl-3,10-dioxa-5-azatricyclo[5.2.1.0^2,6]dec-4-en-9-one ((+)- 5 ) obtained in 6 steps from the Diels-Alder adduct of furan to 1-cyanovinyl (1S)-camphanate ((+)- 3 ) was reduced to the corresponding endo-alcohol (?)- 6 the treatment of which with HBr/AcOH provided (?)-(3aS,4S,6R,7S,7aR)-4β-bromo-3aβ,4,5,6,7,7aβ-hexahydro-2-phenyl-1,3-benzoxazole-6β,7α-diyl diacetate ((?)- 17 ). Elimination of HBr with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and acidic hydrolysis furnished (?)-(1R,2S,3R,4R)-4-aminocyclohex-5-ene-1,2,3-triol ( ? (?)-conduramine C₁;(?)- 1 ).     

Reactions of fused dihydro-1,2,4-thiadiazoles with isocyanates and isothiocyanates to give 6aλ4-thia-1,3,4,6-tetraazapentalene derivatives

3-Methyl-6,7-dihydro-5H-1,2,4-thiadiazolo[4,5-a]pyrimidine 4a reacted with isocyanates and isothiocyanates with elimination of acetonitrile and concomitant addition of two molecules of the heterocumulene to give the 2,3-disubstituted-6,7-dihydro-5H-2aλ⁴-thia-2, 3, 4a, 7a-tetraazacyclopent[cd]indene-1 (2H), 4(3H)-diones 8a–8e and the corresponding dithiones 9a–9h , respectively. 3-Methyl-5, 10-dihydrobenzo[e]-1,2,4-thiadiazolo[4,5-a][1,3]diazepine 5a likewise reacted with isocyanates and isothiocyanates to give the 2,3-disubstituted-5,10-dihydro-2aλ⁴-thia-2,3, 4a, 10a-tetraazapentaleno[3, 3a, 4-gh]benzocyclopheptene-1, 4-diones 10a–10f and the corresponding dithiones 11a–11f . The base 4a reacted with phenyl isocyanate, methyl isothiocyanate, and phenyl isothiocyanate in toluene at room temperature to give the zwitterions 14a , 14b , and 14c , respectively, and the diazepine 5a reacted with phenyl isothiocyanate to give the zwitterion 17 .     

3-Oxo-4,4,4-trifluorobutyronitriles as building blocks of trifluoromethyl substituted heterocycles 2. Heterocyclization to 3-aryl-4-trifluoromethyl-2H-1-benzopyran-2-ones under hoesch reaction conditions

Resorcinol and 5-methylresorcinol, respectively, react with 3-oxo-2-aryl-4,4,4-trifluorobutyronitrile using zinc chloride as a catalyst in dibutyl ether under the Hoesch reaction conditions to give a low yield of 3-aryl-7-hydoxy-4-trifluoromethyl- or 3-aryl-5-hydroxy-7-methyl-4-trifluoromethyl-2H-l-benzopyran-2-ones. However, the related reaction with m-methoxyphenol was found to produce poor yields of 3-aryl-7-methoxy-4-trifluoromethyl-2H-1-benzopyran-2-one and its 3,4-dihydro-4-hydroxy derivative.     

A Ring Enlargement from Seven- to Ten-Membered-Ring sulfonamide derivatives

The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1a ) with 4,5-dihydro-7,8-dimethoxy-1,2-benzothiazepin-3-one 1,1-dioxide ( 4 ) in dioxane at room temperature gave the correspondingly substituted 4H-1,2,5-benzothiadiazecin-6-one 1,1-dioxide 5a in 64% yield (Scheme 2). The structure of this novel ten-membered ring-enlargement product was established by X-ray crystallography (Fig.). Under more vigorous conditions (refluxing dichloroethane), 5a was formed together with the isomeric 6a , both in low yield. The 3-(dimethylamino)-2H-azirines 1b and 1c reacted sluggishly to give the two isomeric ring-enlargement products of type 5 and 6 in yields of 24–29% and 2–4%, respectively (Table 1). Even less reactive is 2,2-dimethyl-3-(N-methyl-N-phenylamino)-2H-azirine ( 1d ), which reacted with 4 in MeCN only at 65°. Under these conditions, besides numerous decomposition products, only traces of 5d and 6d were formed. No ring enlargement was observed with the sterically crowded 1e , which bears an isopropyl group at C(2).     

Breaking the Mirror: pH‐Controlled Chirality Generation from a meso Ligand to a Racemic Ligand

To study the conversion from a meso form to a racemic form of tetrahydrofurantetracarboxylic acid (H₄L), seven novel coordination polymers were synthesized by the hydrothermal reaction of Zn(NO₃)₂ ? 6 H₂O with (2S,3S,4R,5R)‐H₄L in the presence of 1,10‐phenanthroline (phen), 2,2′‐bipyridine (2,2′‐bpy), or 4,4′‐bipyridine (4,4′‐bpy): [Zn₂{(2S,3S,4R,5R)‐L}(phen)₂(H₂O)] ? 2 H₂O ( 1 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L}(phen)₂(H₂O)₂] ( 2 ), [Zn₂{(2S,3S,4R,5R)‐L}(H₂O)₂] ? H₂O ( 3 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L} (2,2′‐bpy)₂(H₂O)₂] ? 2 H₂O ( 4 ), [Zn₂ {(2S,3S,4R,5R)‐L}(2,2′‐bpy)(H₂O)] ( 5 ), [Zn₄{(2S,3R,4R,5R)‐L}{(2S,3S,4S,5R)‐L} (4,4′‐bpy)₂(H₂O)₂] ( 6 ), and [Zn₂ {(2S,3S,4R,5R)‐L}(4,4′‐bpy)(H₂O)] ? 2 H₂O ( 7 ). These complexes were obtained by control of the pH values of reaction mixtures, with an initial of pH 2.0 for 1 , 2.5 for 2 , 4 , and 6 , and 4.5 for 3 , 5 , and 7 , respectively. The expected configuration conversion has been successfully realized during the formation of 2 , 4 , and 6 , and the enantiomers of L, (2S,3R,4R,5R)‐L and (2S,3S,4S,5R)‐L, are trapped in them, whereas L ligands in the other four complexes retain the original meso form, which indicates that such a conversion is possibly pH controlled. Acid‐catalyzed enol–keto tautomerism has been introduced to explain the mechanism of this conversion. Complex 1 features a simple 1D metal–L chain that is extended into a 3D supramolecular structure by π–π packing interactions between phen ligands and hydrogen bonds. Complex 2 has 2D racemic layers that consist of centrosymmetric bimetallic units, and a final 3D supramolecular framework is formed by the interlinking of these layers through π–π packing interactions of phen. Complex 3 is a 3D metal–organic framework (MOF) involving meso‐L ligands, which can be regarded as (4,6)‐connected nets with vertex symbol (4⁵.6)(4⁷.6⁸). Complexes 4 and 5 contain 2D racemic layers and (6,3)‐honeycomb layers, respectively, both of which are combined into 3D supramolecular structures through π–π packing interactions of 2,2′‐bpy. The structure of complex 6 is a 2D network formed by 4,4′‐bpy bridging 1D tubes, which consist of metal atoms and enantiomers of L. These layers are connected through hydrogen bonds to give the final 3D porous supramolecular framework of 6 . Complex 7 is a 3D MOF with novel (3,4,5)‐connected (6³)(4².6⁴)(4².6⁶.8²) topology. The thermal stability of these compounds was also investigated.     

Synthesis of methylpyridine derivatives. XXXV. Reaction of acetylpyridine with phosphoryl chloride to give alkynylpyridine

Reaction of 3-acetyl-4,6-dimethyl-2-(1H)pyridone ( 9a ) with phosphoryl chloride gives 2-chloro-3-ethynyl-4,6-dimethylpyridine ( 10a ). 3-Acetyl-4-hydroxy-6-methyl-2(1H)pyridone (14a) and 3-acetyl-2,6-dimethyl-4-(1H)-pyridone (21) undergoes similar reaction to give the corresponding ethynyl (16 and 23) and chlorovinyl (15 and 22) pyridines, respectively. The chlorination of 3-acetylpyridine and pyrimidine derivatives is further described.     

Photocycloaddition of Isocoumarins and Isothiocoumarins to Alkenes

On irradiation in the presence of tetrachloroethene (TCE), both isocoumarins 3 and isothiocoumarins 4 afford in high yields the cis‐fused cycloadducts 8 and 9 , while only the oxacycles 3 undergo photocycloaddition to 2,3‐dimethylbut‐2‐ene (TME) to give mixtures of cis‐ and trans‐fused products 10 and 11 , respectively, in moderate yields. This higher efficiency in reacting with TCE as compared to TME for compounds 3 and 4 contrasts the behavior of simple cyclic enones, e.g., 5,5‐dimethylcyclohex‐2‐enone ( 12 ), which is converted to bicyclooctanones about fifty times faster with TME than with TCE.     

Pyridine nucleosides related to 5-fluorouracil

5-Fluoro-2-methoxypyridine ( 3 ) synthesized from 5-amino-2-methoxypyridine was converted to 4-benzyloxy-5-fluoro-2-methoxypyridine ( 12 ) and 2,4-dimethoxy-5-fluoropyridine ( 13 ) by a four step procedure employing the intermediate 5-fluoro-2-methoxy-4-nitropyridine N-oxide (7). Condensation of 3 , 12 , and 13 with 2,3,5-tri-O-benzoyl-D -ribofuranosyl bromide gave, after removal of the protecting groups, 4-deoxy-5-fluoro-3-deazauridine (20), 5-fluoro-3-deazauridine (23) and 5-fluoro-4-methoxy-3-deazauridine (25). Several alkylated and dealkylated derivatives of 3 and 12 were also prepared. Structure proof and anomeric configuration were determined from the uv, nmr, and CD data.     

Photoisomerization of 2H,6H-thiin-3-one 1-oxides to 3H,7H-[1,2]oxathiepin-4-ones

Oxidation of 2H, 6H-thiin-3-ones 1a – c with 3-chloroperbenzoic acid affords the corresponding 1-oxides 2a – c . On irradiation (350 nm) in either benzene or MeCN, these cyclic sulfoxides 2 isomerize to 3H, 7H-1,2-oxathiepin-4-ones 3 . The tetramethyl derivative 3a is isolated by flash chromatography at ?10°, but, at higher temperatures, it undergoes ring contraction and H₂O elimination to give 4,4-dimethyl-2(2-methylprop-2enylidene)thietan-3-one ( 4 ). Diemthyloxathiepinones 3b and 3c undergo ring contraction in MeOH to afford 1-(4-methylthiophen-2-yl)ethanone ( 5 ) and two diastereoisomeric 4,4-dimethyl-2-methoxy-2-(1-methoxyethyl)thietan-3-ones ( 6 and 7 , respectively).