Synthesis of polyfunctionalized furans from 3-acetyl-1-aryl-2-pentene-1,4-diones

The BF₃-catalyzed cyclization of 3-acetyl-1-aryl-2-pentene-1,4-diones 1a-e in the presence of water in boiling tetrahydrofuran gave bis(3-acetyl-5-aryl-2-furyl)methanes 2a-e in 26-79% yields along with a small amount of 3-acetyl-5-aryl-2-methylfurans 3a-e. The exact structure of 2a was determined by X-ray crystallography. The use of a half volume of the solvent for the reaction of 1a resulted in the formation of 2,4-bis(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-phenylfuran (4) together with 2a and 3a. A similar reaction of 1a was carried out in the presence of 3-acetyl-5-(4-methylphenyl)-2-methylfuran (3d) to afford 4-(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-(4-methylphenyl)-2-methylfuran (5) in 49% yield. The BF₃-catalyzed reaction of 1a with 2,4-pentanedione in dry tetrahydrofuran at 23°C gave 3-(3-acetyl-5-phenyl-2-furfuryl)-4-hydroxy-3-penten-2-one (6a) and 3-(3-acetyl-2-methyl-4-phenyl-5-furyl)-4-hydroxy-3-penten-2-one (7a) in 66 and 24% yields, respectively. The product distribution depended on the reaction temperature. A similar reaction of 1b-e also yielded the corresponding trisubstituted furans 6b-e and tetrasubstituted furans 7b-e in good yields. These results suggested the presence of the furfuryl carbocation intermediate A during the reaction. The one-pot synthesis of 6a and 7a was also achieved by a similar reaction using phenylglyoxal. The deoxygenation of 1a with triphenylphosphine gave 3a in 88% yield, while 1a was treated with concentrated hydrochloric acid to yield 3-acetyl-2-chloromethyl-5-phenylfuran (8) which was quantitatively transformed in ethanol into 3-acetyl-2-ethoxymethyl-5-phenylfuran (9) and in water into 3-acetyl-5-phenylfurfuryl alcohol (10), respectively. In addition, the Diels-Alder reaction of cyclopantadiene with 1a gave the corresponding [4+2] cycloaddition products 11 and 12.     

The conversion of 2-cyano cyanothioformanilides into 3-aminoindole-2-carbonitriles using triphenylphosphine

2-Cyano cyanothioformanilide 3a reacts with triphenylphosphine in the presence of water to give 2-(cyanomethyleneamino)benzonitrile 4a, 2-(cyanomethylamino)benzonitrile 5, 3-aminoindole-2-carbonitrile 2a and (2-cyanoindol-3-yl)iminotriphenylphosphorane 6a. In the presence of p-toluenesulfonic acid in MeOH the reaction between 2-cyano cyanothioformanilide 3a and triphenylphosphine (2 equiv) gives 3-aminoindole-2-carbonitrile 2a in 90% yield. Under the same conditions 2-(cyanomethyleneamino)benzonitrile 4a gives anthranilonitrile 8a, 3-aminoindole-2-carbonitrile 2a and N-(2-cyanophenyl)formamide 9. In addition, substituted 2-cyano cyanothioformanilides 3b-f react with triphenylphosphine and p-toluenesulfonic acid in MeOH to give 3-aminoindole-2-carbonitriles 2b-f in 63-75% yields. Under analogous conditions 2-cyano-4,5-dimethoxyphenyl cyanothioformanilide 2g gives only 4,5-dimethoxyanthranilonitrile 8g and 4,6,7-trimethoxyquinazoline-2-carbonitrile 14g, but in refluxing dry PhMe in the absence of p-toluenesulfonic acid 2-cyano-4,5-dimethoxyphenyl cyanothioformanilide 3g, (2-cyano-5,6-dimethoxyindol-3-yl)iminotriphenylphosphorane 6g and 2-(cyanomethyleneamino)-4,5-dimethoxybenzonitrile 4g are obtained. The structure of 2-(cyanomethyleneamino)-4,5-dimethoxybenzonitrile 4g is supported unambiguously via independent synthesis and comparison to the isomeric 6,7-dimethoxyquinazoline-2-carbonitrile 15. All new compounds are fully characterised and a tentative mechanism for the transformation of 2-cyano cyanothioformanilides to indoles is proposed.     

An efficient microwave assisted synthesis of novel class of Rhodanine derivatives as potential HIV-1 and JSP-1 inhibitors

(Z)-5-(2-(1H-Indol-3-yl)-2-oxoethylidene)-3-phenyl-2-thioxothiazolidin-4-one (7a-q) derivatives have been synthesized by the condensation reaction of 3-phenyl-2-thioxothiazolidin-4-ones (3a-h) with suitably substituted 2-(1H-indol-3-yl)-2-oxoacetaldehyde (6a-d) under microwave condition. The thioxothiazolidine-4-ones were prepared from the corresponding aromatic amines (1a-e) and di-(carboxymethyl)-trithiocarbonyl (2). The aldehydes (6a-h) were synthesized from the corresponding acid chlorides (5a-d) using HSnBu₃.     

Synthesis of novel lariat azathia crown macrocycles containing two triazole rings and bis crown macrocycles containing four triazole rings

The 13-hydroxy macrocycles 7a-d were prepared in 40-50% yields by the condensation of 1,ω-bis(4-amino-1,2,4-triazol-3-ylsulfany)alkanes 2a-d with 1,3-bis(2-formyphenoxy)-2-propanol (9). Acylation of 7a-d with 2-chloroacetylchloride gave the corresponding esters 11a,b. Amination of 11a,b with different amines in acetone furnished exclusively the target lariat macrocycles 12a,b and 13 in 60-70% yields. Reaction of 2 equiv. of the macrocycles 11a,b with 1 equiv. of piperazine afforded the novel bis macrocyles 14a,b in 50-60% yields. Reduction of 7a-d with NaBH₄ afforded the corresponding 13-hydroxyazathia crown ethers 15a-d in 65-70% yields.     

Sodium dithionite initiated reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane with enol ethers of cyclic ketones

Sodium dithionite initiated reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane (1) with methyl and trimethylsilyl ethers of cyclopentanone and cyclohexanone enols (2a-d) in a MeCN/H₂O system were investigated. 2-(2,2,2-Trifluoroethylidene)cyclopentanone (4a) and 2-(2,2,2-trifluoroethylidene)-cyclohexanone (4b), respectively, were obtained as the main products and isolated in reasonable yields. The reaction with a 1:1 mixture of 5- and 3-methyl substituted 1-methoxycyclohexenes, 2e and 2f, revealed strong influence of steric hindrance on the reaction rate; a mixture of 2-(2,2,2-trifluoroethylidene)-5-methylcyclohexanone (6) and 2-(2,2,2-trifluoroethylidene)-3-methylcyclohexanone (7) in a 9:1 ratio was formed. Ketones 4a and 4b were reduced to the corresponding alcohols 8 and 9 and the reaction of 4b with hydrazine gave an indazole derivative 10.     

Highly efficient synthesis of phenanthroquinolizidine alkaloids via Parham-type cycliacylation

A concise and efficient route involving Parham-type cycliacylation as the key step has been used to synthesize phenanthroquinolizidine alkaloids 1a-c and 2a-c. Among the products, 1b-(S), 1b-(R), 2a-(14aS,15S), 2a-(14aR,15R), and 2b were synthesized for the first time.     

Manganese(III) acetate based oxidative cyclizations of 3-oxopropanenitriles with conjugated alkenes and synthesis of 4,5-dihydrofuran-3-carbonitriles containing heterocycles

4,5-Dihydrofuran-3-carbonitriles 3a-i were obtained through oxidative cyclizations of 3-oxo-3-phenylpropanenitrile 1a, 3-oxo-3-thien-2-ylpropanenitrile 1b, 3-(2-furyl)-3-oxopropanenitirle 1c, 3-(1-benzofuran-2-yl)-3-oxopropanenitrile 1d, and 4,4-dimethyl-3-oxopropanenitrile 1e mediated manganese(III) acetate with 1,1-diphenyl-1-butene 2a and 1,2-diphenyl-1-pentene 2b. The treatments of these 3-oxopropanenitriles with 2-thienyl substituted alkenes such as 2-[(E)-2-phenylvinyl]thiophene 2c, 2-[(E)-1-methyl-2-phenylvinyl]thiophene 2d, and 2-(1-phenylvinyl)thiophene 2e formed 5-(2-thienyl)-4,5-dihydrofuran-3-carbonitriles 3j-r in good yields (45-93%). As a result, 2-thienyl substituted alkenes formed products in higher yields than phenyl substituted derivatives.     

Fluorinated molecules relevant to conducting polymer research

The synthesis of versatile fluorine compounds for conducting polymer research on fluorinated materials is presented. 1,2,4,5-Tetrafluorobenzene was converted to 1,2,4,5-tetrafluorobenzaldehyde (1) and protected as an acetal. This gave the acetals 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)benzene (2a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)benzene (2b). Compounds 2a and 2b were converted into the semiprotected 2,3,5,6-tetrafluoroterephthaldehydes: 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)-6-formylbenzene (3a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-6-formylbenzene (3b). While 3a was easily deprotected to give 2,3,5,6-tetrafluoroterephthaldehyde (4) compound 3b proved very resilient to hydrolysis and gave a 1:1 mixture of 4 and 1,2,4,5-tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-2-yl)benzene (5). Compound 4 was reduced to 1,2,4,5-tetrafluoro-3,6-dihydroxymethylbenzene (6) and converted into 1,2,4,5-tetrafluoro-3,6-dibromomethylbenzene (7). Compound 7 was finally converted into 1,2,4,5-tetrafluoro-3,6-bis(diethylphosponylmethyl)benzene (8). Compounds 4 and 8 are versatile fluorinated molecules that can be used to replace their hydrogen counterparts in many molecules and materials. To illustrate this compounds 4 and 8 were oligomerised to give partially fluorinated polyphenylenevinylene (9).     

Preparation of new pyrido[3,4-b]thienopyrroles and pyrido[4,3-e]thienopyridazines

Two new types of pyrido-fused tris-heterocycles (1a,b and 2a,b) have been prepared from 3-aminopyridine in five/six steps. A synthetic strategy for the preparation of the novel pyrido[3,4-b]thieno[2,3- and 3,2-d]pyrroles (1a,b) and pyrido[4,3-e]thieno[2,3- and 3,2-c]pyridazines (2a,b) has been studied. The Suzuki cross coupling of the appropriate 2- and 3-thienoboronic acids (3,4) and 4-bromo-3-pyridylpivaloylamide (9) afforded the biaryl coupling products (10,11) in high yields (85%). Diazotization of the hydrolysed (2-thienyl)-coupling product (12) and azide substitution gave the 3-azido-4-(2-thienyl)pyridine intermediate (72%, 14). 3-Azido-4-(3-thienyl)pyridine (15) was prepared by exchanging the previous order of reactions. The desired β-carboline thiophene analogues (1a,b) were obtained via the nitrene by thermal decomposition of the azido precursors (14,15). By optimising conditions for intramolecular diazocoupling, the corresponding pyridazine products (72-83%, 2a,b) were afforded.     

Zn-promoted regio- and sequence-selective one-pot joining reactions of three components: vinylpyridines, alkyl iodides, and carbonyl compounds (or nitriles)

Addition of alkyl iodides (3) into the solution containing 2-(or 4-)vinylpyridine (1 or 2) and carbonyl compounds (6) in the presence of Zn-powder (99.9%) in acetonitrile under refluxing brought about regio- and sequence-selective joining reaction of three components to give the corresponding (2-hydroxyethyl)pyridines (7 or 8) in good to moderate yields. On the other hand, 2-(2- or 4-pyridyl)ethyl alkyl ketones (10 or 11) were obtained from the similar joining reaction of three components by addition of alkyl iodides (3) into the solution of 2-(or 4-)vinylpyridine (1 or 2), and nitriles (9) in toluene containing Zn-powder (99.9%) under the similar reaction conditions.     

Catalyst- and steric-controlled alkenylation via chemoselective C-H activation and C-Br activation in Heck reaction of methyl 1-(2-bromoaryl)-3-(2-furyl/thienyl)-5-oxopyrrolidine-2-carboxylates and diethyl 1-(2-bromoaryl)-3-(2-furyl/thienyl)-5-oxopyrrolidine-2,2-dicarboxylate derivatives

Pd(II)-catalyzed alkenylation of methyl 1-(2-bromoaryl)-3-(2-furyl/thienyl)-5-oxopyrrolidine-2-carboxylate derivatives 1(a-d) resulted in the formation of 3(a-d) exclusively via C-H activation in the heteroaryl moiety. Similar observations were observed for the corresponding diester analogues 4(a-d) to form 5(a-d). Normal Heck reaction, however, was observed in the case of 1(a-f) to furnish 2(a-f) when the reaction was carried out with Pd(0) catalyst generated in situ. Pd(0)-catalyzed vinylation of 4(a-f) via C-Br oxidation, however, failed due to steric reason.     

Microwave-assisted manganese(III) acetate based oxidative cyclizations of alkenes with β-ketosulfones

The microwave-assisted synthesis of 5-(4-nitrophenyl)-2-phenyl-4-(phenylsulfonyl)-2,3-dihydrofuran (5a) was performed via manganese(III) acetate based oxidative cyclization of 1-(4-nitrophenyl)-2-(phenylsulfonyl)ethanone (3a) with vinylbenzene (4a). This new protocol was applied to four sulfone derivatives (3a-d), using vinylbenzene (4a) and diphenylethene (4b), affording a series of 2,3-dihydrofurans (5a-d, 6a-d) in moderate to good yields (26-55%). Similar methodology, applied on allylbenzene (4c), surprisingly, led to dehydronaphthalene derivatives (7a-d) in moderate yields. The unexpected mechanism and the role of allylbenzene (4c) are herein discussed.     

Photobehaviour of 2- and 3-heteroaryl substituted o-divinylbenzenes; formation of fused 2,3- and 3,2-heteroareno-benzobicyclo[3.2.1]octadienes and 3-heteroaryl benzobicyclo[2.1.1]hexenes

New β-3-thienyl (8) and β-3-furyl derivatives of o-divinylbenzene (9) have been synthesised and their photochemical behaviour compared with 2-thienyl (7) and 2-furyl derivatives (2). Whereas the β-(2-heteroaryl) substituted o-divinylbenzenes (7 or 2) give only bicyclo[3.2.1]octadiene structure (14 or 1) by 1,6-ring closure of the biradical intermediate, β-(3-heteroaryl) substituted o-divinylbenzenes (8 or 9) give bicyclo[3.2.1]octadiene structure (23 or 24) and bicyclo[2.1.1]hexene structure (25 or 26) by 1,6- and 1,4-ring closure, respectively. This photochemical approach provides a simple method to 2,3- and 3,2-fused thiophene and furan polycyclic compounds.     

Reactions of azulenes with 1,2-diaryl-1,2-ethanediols in methanol in the presence of hydrochloric acid: comparative studies on products, crystal structures, and spectroscopic and electrochemical properties

Although reaction of guaiazulene (1a) with 1,2-diphenyl-1,2-ethanediol (2a) in methanol in the presence of hydrochloric acid at 60 °C for 3 h under aerobic conditions gives no product, reaction of 1a with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol (2b) under the same reaction conditions as 2a gives a new ethylene derivative, 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (3), in 97% yield. Similarly, reaction of methyl azulene-1-carboxylate (1b) with 2b under the same reaction conditions as 1a gives no product; however, reactions of 1-chloroazulene (1c) and the parent azulene (1d) with 2b under the same reaction conditions as 1a give 2-[3-(1-chloroazulenyl)]-1,1-bis(4-methoxyphenyl)ethylene (4) (81% yield) and 2-azulenyl-1,1-bis(4-methoxyphenyl)ethylene (5) (15% yield), respectively. Along with the above reactions, reactions of 1a with 1,2-bis(4-hydroxyphenyl)-1,2-ethanediol (2c) and 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol (2d) under the same reaction conditions as 2b give 2-(3-guaiazulenyl)-1,1-bis(4-hydroxyphenyl)ethylene (6) (73% yield) and (Z)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1-phenylethylene (7) (17% yield), respectively. Comparative studies of the above reaction products and their yields, crystal structures, spectroscopic and electrochemical properties are reported and, further, a plausible reaction pathway for the formation of the products 3-7 is described.     

Synthesis of nicotinonitrile derivatives as a new class of NLO materials

4,6-Diaryl-2-(pyrrolidin-1-yl)-nicotinonitriles 2a-k and 3-amino-2,4-dicyano-5-aryl-biphenyls 3a-c were synthesized from 1,3-diaryl-prop-2-en-1-ones 1a-k and malononitrile by a convenient one-pot method. Likewise, the reaction of aromatic aldehydes with malononitrile afforded 6-amino-4-aryl-2-(pyrrolidin-1-yl)-pyridine-3,5-dicarbonitriles 6a-f. The reaction of mesityl oxide with malononitrile gave 5-amino-7-(pyrrolidin-1-yl)-2,4,4-trimethyl-1,4-dihydro-1,6-naphthyridine-8-carbonitrile 8. The NLO studies of the pyridinedinitrile derivatives 6a, b, f showed a high value while that of nicotinonitrile 2b was weak.     

Efficient syntheses of thiadiazoline and thiadiazole derivatives by the cyclization of 3-aryl-4-formylsydnone thiosemicarbazones with acetic anhydride and ferric chloride

3-Aryl-4-formylsydnone 4′-phenylthiosemicarbazones 3a-d and 3-aryl-4-formylsydnone thiosemicarbazones 3e-h are effective precursors of sydnonyl-substituted heterocycles. The thiosemicarbazones 3a-d reacted with acetic anhydride (4a) to give 4-acetyl-2-phenylamino-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles 5a-d and 4-acetyl-2-(N-phenylacetamido)-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles 6a-d. However, under similar method, thiosemicarbazones 3e-h produced only 4-acetyl-2-acetamido-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles 6e-h in high yield. The sydnonyl-substituted thiadiazole derivatives 7a-h were also obtained successfully by the cyclization of 3-aryl-4-formylsydnone thiosemicarbazones 3a-h with ferric chloride (4b). In the cyclization, the thiosemicarbazones 3a-d are more reactive than the thiosemicarbazones 3e-h.     

Polybrominated diphenyl ethers (BDEs); preparation of reference standards and fluorinated internal analytical standards

Four new difluorinated tetra- and pentabromo BDE internal standards for GC-MS/GC-ECD analysis, 2F-BDE47, 2F-BDE85, 2F-BDE99 and 2F-BDE119, have been prepared in 98-99.0% purity, mainly by coupling of the new tribromodifluorophenols (19-21) and symmetrical bromodiphenyliodonium salts (8, 22). The four difluorinated BDEs showed promising properties as internal standards for quantitative BDE analysis. Tetra-, penta-, hexa- and hepta-brominated BDE reference standards, BDE75, BDE85, BDE138 and BDE183, were also prepared in 98.4-99.8% purity and characterised.     

Microwave-assisted synthesis of novel bis(2-thioxothiazolidin-4-one) derivatives as potential GSK-3 inhibitors

(5Z,5′Z)-3,3′-(1,4-Phenylenebis(methylene)-bis-(5-arylidene-2-thioxothiazolidin-4-one) derivatives (5a-r) have been synthesized by the condensation reaction of 3,3′-(1,4- or 1,3-phenylenebis(methylene))bis(2-thioxothiazolidin-4-ones) (3a,b) with suitably substituted aldehydes (4a-f) or 2-(1H-indol-3-yl)2-oxoacetaldehydes (8a-c) under microwave conditions. The bis(2-thioxothiazolidin-4-ones) were prepared from the corresponding primary alkyl amines (1a,b) and di-(carboxymethyl)-trithiocarbonyl (2). The 2-(1H-indol-3-yl)-2-oxoacetaldehydes (8a-c) were synthesized from the corresponding acid chlorides (7a-c) using HSnBu₃.     

Highly efficient, multigram and enantiopure synthesis of (S)-2-(2,4′-bithiazol-2-yl)pyrrolidine

(S)-2-(4-Bromo-2,4′-bithiazole)-1-(tert-butoxycarbonyl)pyrrolidine ((S)-1) was obtained as a single enantiomer and in high yield by means of a two-step modified Hantzsch thiazole synthesis reaction when bromoketone 3 and thioamide (S)-4 were used. Further conversion of (S)-1 into trimethyltin derivative (S)-2 broadens the scope for further cross-coupling reactions.     

Synthesis of pyridine and 2,2′-bipyridine derivatives from the aza Diels-Alder reaction of substituted 1,2,4-triazines

Amidrazone 1a and the tricarbonyl derivatives 2b-d reacted in boiling ethanol in the presence of 2,5-norbornadiene 5 giving the pyridine derivatives 6b-d respectively (59-72%) and in the presence of 2,3-dihydrofuran 7 yielding the lactones 10b-d (39-44%). The 2,2′-bipyridine derivatives 6e-g were similarly obtained in good yield (81-87%) from the reaction of amidrazone 1b and tricarbonyl derivatives 2b-d in the presence of 2,5-norbornadiene 5.