Enantioselective synthesis of furo[2,3-b]furans, a spongiane diterpenoid substructure

[structure: see text] A short and enantioselective synthesis of cis-fused 5-oxofuro[2,3-b]furans, being found in many spongiane diterpenoid natural products, is reported starting from inexpensive methyl 2-furoate. Moreover, the acid-catalyzed rearrangement of the furo[2,3-b]furan framework A to B is observed for some derivatives, suggesting a simple connection between natural products differing in the absolute configuration of the 3a,6a ring junction.     

A Facile and Efficient Synthesis of Thieno[2,3-c]furans and Furo[3,4-b]indoles via a Pummerer-Induced Cyclization Reaction

The alpha-thiocarbocation generated from the Pummerer reaction of an o-heteroaroyl-substituted sulfoxide is intercepted by the adjacent keto group to produce an alpha-thio-substituted heteroaromatic isobenzofuran. In the presence of a suitable dienophile, the reactive o-xylylene undergoes a Diels-Alder cycloaddition followed by an acid-catalyzed ring-opening and aromatization to give heteroaromatic naphthalene derivatives. This one-pot procedure occurs smoothly with electron-deficient dienophiles. The tandem Pummerer cyclization-cycloaddition sequence also occurs intramolecularly using unactivated alkenyl tethers of variable length. With acetylenic dienophiles, the primary cycloadducts undergo in situ ring-opening to produce hydroxynaphthalene derivatives. In the absence of a dienophile, it was possible to prepare 4-(ethylthio)-6-phenylthieno[2,3-c]furan and 1-ethyl-4-(phenylsulfonyl)-4H-furo[3,4-b]indole. Various synthetic approaches were used for the preparation of the requisite thiophene- and indole-derived sulfoxide precursors. The facility of the tandem Pummerer-Diels-Alder reaction was very dependent on the experimental conditions used to promote the reaction. The best results were achieved by employing a mixture of acetic anhydride and toluene which contained a catalytic quantity of p-toluenesulfonic acid. The presence of the acid effectively drives the reaction in the desired direction by preventing formation of the acetoxy sulfide, which corresponds to the normal Pummerer product.     

Facile synthesis of polysubstituted furans and dihydrofurans via cyclization of bromonitromethane with oxodienes

A series of polysubstituted furans and dihydrofurans have been prepared from readily available oxodienes and bromonitromethane in modest to excellent yields. This facile synthetic method is developed on the basis of proprietary properties of nitro group such as strong electron-withdrawing ability and cleavability. The conversion of nitro-substituted dihydrofurans to furans is presumably realized by elimination of HNO₂ under the aid of DABCO.     

Facile and convenient synthesis of new thieno[2,3-b]-thiophene derivatives

A facile and convenient synthesis of bis(2-(1H-benzo[d]imidazol-2(3H)-ylidene)-3-oxopropanenitrile), bis((3-amino-5-(methylthio)-1H-pyrazol-4-yl)methanone) and bis(2-thioxo-1,2-dihydropyrimidine-5-carbonitrile) derivatives incorporating a thieno- [2,3-b]thiophene moiety via versatile, readily accessible diethyl 3,4-dimethylthieno-[2,3-b]thiophene-2,5-dicarboxylate is described.     

Efficient synthesis of fused perhydrofuro[2,3-b]pyrans (and furans) by ring opening of 1,2-cyclopropanated sugar derivatives

[structure: see text]. An efficient method has been developed for the construction of fused perhydrofuro[2,3-b]pyrans by diastereoselective ring opening of 1,2-cyclopropanated sugar derivatives. The methodology has been successfully applied to the synthesis of fused perhydrofuro[2,3-b]pyrano-gamma-butyrolactone derivatives.     

A simple synthesis of thieno[2,3-b]pyrazine and thieno[2,3-b] pyridine

A facile synthesis of thieno[2,3-b]pyrazine (1) and thieno[2,3-b]pyridine (9) is reported. Furthermore, convenient preparations of a variety of synthetically useful compounds derived from these ring systems is also presented.     

Dearomatization of furans via [2,3]-Still-Wittig rearrangement

Furans and benzofurans of type 1 were dearomatized via the [2,3]-Still-Wittig rearrangement. Enol ethers 2 could be isolated or isomerized to the corresponding furans 3. The substitution pattern at the homofuranylic position had a strong influence on reaction behavior. Benzofurans rearranged with the greatest efficiency, and employment of a 3-substituted benzofuran (1; R′=CH₃) allowed the creation of a quaternary carbon center.     

Facile preparation of benzo[4,5]thieno[2,3-b]pyridines and naphtho[b-4,5]thieno[2,3-b]pyridines via the reaction of Barton esters and benzynes

Titled compounds were prepared in a one-pot synthesis by generating symmetrically substituted benzyne intermediates by the diazotization of anthranilic acids in the presence of Barton esters. Unsymmetrically substituted aryne either gave mixtures of regioisomers or failed. However, nitro and methyl derivatives of titled compounds could be obtained as single products using appropriately substituted Barton esters.     

3-Methyl[1,3,4]thiadiazino[2,3-b]quinazolin-6-ones

4H,6H-[1,3,4]Thiadiazino[2,3-b]quinazolin-6-one with a methyl group in position 3 (6a) has been synthesised by the condensation of 3-amino-2-mercapto-3H-quinazolin-4-one (1) with allyl bromide (2) followed by treatment with bromine and subsequent dehydrohalogenation of the brominated product (4) with ethanolic sodium hydroxide. Its isomeric 3-methyl-2H,6H-[1,3,4]thiadiazino[2,3-b]quinazolin-6-one (6b) has also been obtained by condensation of1 and bromoacetone (7) followed by cyclisation of the intermediates (8 or9) with hydrobromic acid or with concentrated sulphuric acid. The structures have been established on the basis of IR and PMR data.

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3-Methyl[1,3,4]thiadiazino[2,3-b]chinazolin-6-one

Zusammenfassung Zur Synthese von 4H,6H-[1,3,4]thiadiazino[2,3-b]chinazolin-6-on (6a) wurde die Kondensation von 3-Amino-2-mercapto-3H-chinazolin-4-on (1) mit Allylbromid mit nachfolgender Behandlung mit Brom und Dehydrohalogenierung des bromierten Produktes4 mit ethanolischer Natronlauge herangezogen. Das zu6a isomere 2H,6H-Produkt6b wurde ebenfalls durch Kondensation von1 mit Bromaceton und nachfolgender Cyclisierung der Zwischenprodukte8 bzw.9 mit HBr oder H₂SO₄ erhalten. Die Strukturen wurden mittels IR und NMR abgesichert.

     

Synthesis of polyacenequinones via a benzo[2,3-c]furan

1,3-Bis(4-tert-butylphenyl)-4.7-diacetoxybenzo- (2,3-c)furan (3c) serves as a masked-dienophile/diene equivalent, which can elongate a 1,4-quinone by two rings. Elongation Involves a three step sequence of Diels-Alder reaction, dehydrative-aromatization. and oxidative unmasking of the dienophile. This elongation strategy has been used to sequentially convert napthoquinone to a tetracenetetrone and a hexacenetetrone.     

A new one-step synthesis of 2,3-dihydro-5H-thiazolo[2,3-b]quinazolin-5-one and 3,4-dihydro-2h,6h[1,3]thiazino[2,3-b] quinazolin-6-one

2,3-Dihydro-5H-thiazolo[2,3-b]quinazolin-5-one and 3,4-dihydro-2H,6H[1,3] thiazino[2,3-b]-quinazolin-6-one have been synthesized in one step by the reaction of methyl anthranilate with ehloroalkyl isothiocyanates.     

One-pot synthesis of acenaphtho[1,2-b]furan derivatives

New 9-(alkyl or aryl)acenaphtho[l,2-b]furan-8-(alky or aryl)amine compounds has herein been reported by one-pot reaction of (acenaphthylen-l-yloxy)trimethylsilane,alkyl and aryl aldehydes,and aryl and alky isocyanides in refluxing DMF.     

The synthesis of substituted 2,3-dihydrothieno[2,3-b]-thiophenes via intramolecular michael addition

The first regiospecific synthesis of the 2,3-dihydrothieno[2,3-b]thiophene ring system was achieved using an intramolecular Michael addition in the key cyclization step. This strategy represents a novel and potentially general method for dihydrothiophene and dihydrothiophene S,S-dioxide annellation.     

Synthesis of 3a,6,6,9a-tetramethyl-trans-perhydronaphtho [2,1-b]furan and 4a,7,7,10a-tetramethyl-trans-perhydronaphtho [2,1-b]pyran

The compounds 3a,6,6,9a-tetramethyl-trans-perhydronaphtho[2,1-b]furan (ambrox or ambroxide) and 4a,7,7,10a-tetramethyl-trans-perhydronaphtho[2,1-b]pyran (homofixator) — substances important in the perfume industry — have been synthesized by superacid cyclization of E,E-homofarnesol and E,E-bishomofarnesol or mixtures of the isomeric bicyclohomofarnesenes or bicyclobishomofarnesenols. Superacid cyclization of these alcohols was shown to be an effective structurally selective and stereospecific method of obtaining ambroxide and homofixator.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 896–901, July, 1990.     

The synthesis of 5,6-dihydro-6-methylthiazolo-[2,3-b] [1,3] benzodiazepines, 2,3,10,11-tetrahydro-10-methyl-1H-cyclopenta[4,5] thiazolo[2,3-b] [1,3] benzodiazepine,and 7,8,9,10,12,13-hexahydro-13-methylbenzothiazolo[2,3-b] [1,3]-benzodiazepine via 1,3,4,5-tetrahydro-5-methyl-2H-1,3-benzodiazepine-2-thione

Catalytic reductive scission of 4-methylcinnoline (V) with Raney nickel afforded o-amino-β-methylphenethylamine (IV) in 57% yield. Treatment of IV with carbon disulfide followed by thermal cyclization of the product furnished 1,3,4,5-tetrahydro-5-methyl-2H-1,3-benzodiazepine-2-thione (III). Reaction of III with ethyl chloroacetate, ethyl 2-bromohexanoate, ethyl 2-chloroacetoacetate, 2-bromo-2′-methoxyacetophenone, and 2-bromoacetophenone provided a series of substituted 5,6-dihydro-6-methylthiazolo[2,3-b][1,3]benzodiazepines. Condensation of III with 2-chlorocyclopentanone and 2-chlorocyclohexanone gave 2,3,10,11-tetrahydro-10-methyl-1H-cyclopenta[4,5]thiazolo[2,3-b][1,3]benzodiazepine and 7,8,9,10,12,13-hexahydro-13-methylbenzothiazolo[2,3-b][1,3]benzodiazepine, respectively. Structure assignments are discussed. None of the compounds possessed appreciable biological activity.     

Ionic Liquid-Mediated Facile Synthesis and Antimicrobial Study of Thiazolo [2,3-b]Benzo[h]Quinazolines and Thiazino[2,3-b] Benzo-[h]Quinazolines

Abstract

8-Methoxy-4-phenyl-3,4,5,6-tetrahydrobenzo[h]quinazoline-2(1H)-thione, obtained by the condensation of 2-benzylidene-6-methoxy-3,4-dihydronapthalene-1(2H)-one with thiourea, on reaction with chloroacetic acid and 3-chloropropanoic acid in the presence of the ionic liquid N-methylpyridinium tosylate furnishes 3-methoxy-7-phenyl-7,10-dihydro-5H- benzo[h]thiazolo[2,3-b]quinazoline-9(6H)-one and 3-methoxy-7-phenyl-5,6,10,11-tetrahydro- benzo[h][1,3]thiazino[2,3-b]quinazoline-9(7H)-one. Further, condensation of the thione with 1,2-dibromoethane and 1,3-dibromopropane yields 3-methoxy-7-phenyl-6,7,9,10-tetrahydro-5 H-benzo[h]thiazolo[2,3-b]quinazoline and 3-methoxy-7-phenyl-5,6,7,9,10,11-hexahydrobenzo [h][1,3]thiazino[2,3-b]quinazoline respectively. Arylidene derivatives have been obtained by two routes. The structures of the cyclized compounds have been established on the basis of elemental analysis and spectroscopic data. The synthesized compounds were screened for antimicrobial activity. Some of the compounds showed promising antimicrobial activities.