Annulation reaction of methyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate with β-nitrostyrenes and 3-nitrochromenes

The acid catalyzed domino reaction of β-nitrostyrenes with methyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate, which were previously prepared from the cyclization of 2-aminobenzenethiol and methyl 4-chloroacetoacetate, resulted in 2-arylbenzo[b]pyrrolo[1,2-d][1,4]thiazine-3-carboxylates in high yields. Under same reaction conditions, the similar reaction with 3-nitrochromenes afforded corresponding benzo[b]chromeno[4′,3':4,5]pyrrolo[1,2-d][1,4]thiazine derivatives in good yields.     

A facile synthesis of benzo[b][1,4]thiazepine derivatives by palladium acetate catalyzed reaction

The preparation of steroid/nonsteroid fused benzo[b][1,4]thiazepines and 2-arylsubstituted benzo[b][1,4]thiazepines is described from Pd(OAc)₂ catalyzed reaction of steroidal/nonsteroidal β-halovinyl aldehydes and 2-aminothiophenols in DMF under heating condition.     

Microwave-assisted one-pot synthesis of benzo[b][1,4]oxazin-3(4H)-ones via Smiles rearrangement

An efficient method for the synthesis of benzo[b][1,4]oxazin-3(4H)-ones via Smiles rearrangement using a microwave-assisted one-pot, three-step reaction has been developed. Various benzo[b][1,4]oxazin-3(4H)-ones are obtained in good yields (55-86%) from the corresponding substituted 2-chlorophenols and primary amines in short reaction time (18-40 min).     

An unexpected route toward the synthesis of spiro-benzo[b]acridine-furan derivatives

A facile and straightforward procedure for the synthesis of spiro-benzo[b]acridine-6,2′-furan derivatives via the reaction between benzo[b]acridine-6,11-dione, electron-deficient acetylenic compounds, and an isocyanide is described. The benzo[b]acridine-6,11-dione is obtained from the reaction between 2-(aminomethyl)aniline and 2-hydroxynaphthalene-1,4-dione via an unexpected reaction pathway. The products are synthesized in medium to high yields and no complicated purification is required.     

New ‘2-phenylnaphthalene’-mediated synthesis of benzo[b]naphtho[2,3-d]furan-6,11-diones and 6-oxa-benzo[a]anthracene-5,7,12-triones: first total synthesis of 6-oxa-benzo[a]anthracen-5-ones

We describe here a novel synthesis of benzo[b]naphtho[2,3-d]furan-6,11-diones based on the heteroannulation of 2-(2-bromophenyl)-3-hydroxy-1,4-naphthoquinones. The naphthoquinones were prepared from 3-(2-bromophenyl)naphthalen-2-ols, which were obtained by intramolecular aldol condensation of 2-[3-(2-bromophenyl)-2-oxo-propyl]benzaldehydes. Alternatively, benzo[b]naphtho[2,3-d]furan-6,11-diones were obtained more directly and efficiently by cyclization of 3-(2-bromophenyl)naphthalen-2-ols to benzo[b]naphtho[2,3-d]furans and oxidation of the resulting compounds. Furthermore, the first 6-oxabenzo[a]anthracen-5-one described was similarly obtained from 2-[3-(2-formylphenyl)-2-oxopropyl]benzoic acid and oxidized to 6-oxa-benzo[a]anthracene-5,7,12-trione.     

A modular CuI-L-proline catalyzed one-pot route for the rapid access of constrained and privileged hetero-atom-linked medium-sized ring systems

An efficient CuI-L-proline catalyzed one-pot synthesis was developed to generate a collection of skeletally diverse heterocyclic ring systems with sizes ranging from 6 to 9. A salient feature of this design strategy is its modular synthetic utility using an S_N2 reaction followed by a microwave assisted CuI-L-proline hetero-arylation, which has granted access to a series of heterocyclic frameworks including: benzo[e]pyrrolo[1,2-a][1,4]diazepin, benzo[e]pyrrolo[1,2-a][1,4]diazocin, benzo[e]pyrido[1,2-a][1,4]diazocinones, dibenzo[b,f][1,5]diazoninones, dihydrodibenzo[b,e][1,4]thiazepine, dibenzo[b,e][1,4]thiazocine and benzo[6,7][1,4]diazepino[1,2-a]indole. Moreover, the synthetic procedures described herein, allows rapid entries to synthetically challenging medium-sized heterocyclic systems with good overall yields.     

A new methodology of annelation of five- and seven-membered heterocycles to quinoxalines

Pyrazolo[3,4-b]-, isoxazolo[4,5-b]-, benzo[2,3]-1,4-diazepino-, and benzo[2,3]-1,4-oxazepinoquinoxalines were prepared by reactions of 2-quinoxalinecarboxaldehyde with 1,2-N,N-, 1,2-N,O and 1,4-N,N- and 1,4-N,O-dinucleophiles.     

Recent advances in the synthesis of benzo[b]thiophene fused polycyclic derivatives: Strategies and reactions

Benzo[b]thiophene fused compounds with a unique active heterocyclic skeleton have wide applications in the fields of medicinal chemistry, organic synthesis, and organic functional materials, which resulted in rapid development of many efficient methods for the construction of benzo[b]thiophene-fused heterocycles in recent years. Among these methods, the domino reaction of benzo[b]thiophene derivatives is a practical and powerful synthetic route to access benzo[b]thiophene-fused heterocycles by virtue of the particularity of sulfur atom. This review summarizes the latest developments in the construction of benzo[b]thiophene-fused heterocycles by ring formation at the C2-C3-position of benzo[b]thiophene derivatives in the past decade. Additionally, this review is divided into four parts according to the four kinds of benzo[b]thiophene derivatives used, including thioaurone, thioisatin, substituted benzo[b]thiophene, and azadiene.     

Synthesis of 9-nitro-5H-spiro[benzo[b]tetrazolo[1,5-d][1,4]oxazepine-4,2′-oxirane] via an unusual ring-expansion

Attempted cyclization of (4-(hydroxymethyl)-8-nitro-4H-benzo[b]tetrazolo[1,5-d][1,4]oxazin-4-yl)methyl 4-methylbenzenesulfonate 2 did not give the expected spirooxetane product 1, but instead provided 9-nitro-5H-spiro[benzo[b]tetrazolo[1,5-d][1,4]oxazepine-4,2′-oxirane] 3via an unusual ring-expansion process. The structure of compound 3 was confirmed by single-crystal X-ray crystallography. The spiroepoxide (oxirane) in compound 3 could be ring-opened with a variety of nucleophiles to give products of potential interest to medicinal chemists.     

Synthesis of some heterocyclic skeletons via organoiron complexes. Crystal and molecular structure of (5a,6,7,8,9,9a-η6-1,4-benzoxathiino[3,2-b]pyridine)(η5-cyclopentadienyl)iron hexafluorophosphate

Synthesis of the heterocyclic skeletons of some biologically active compounds from (η⁶-o-dichlorobenzene)(η⁵-cyclopentadienyrl)iron hexafluorophosphate in a two step procedure is described. Cyclopentadienyliron hexafluorophosphate complexes of 1,4-benzodioxino[2,3-b]pyridine, 1,4-benzoxathiino[3,2-b]pyridine, 10H-pyrido[3,2-b]benzoxazine, benzo[b]naphtho[2,3-e][1,4]dioxin, 4-methylbenzo[b]benzopyran-2-one[7,6-e][1,4]dioxin and benzo[b]anthracen-9,10-diono[1,2-e][1,4]dioxin were isolated and characterized. Upon pyrolytic sublimation of these complexes the free heterocycles were obtained and characterized. (η⁶-1,4-Benzoxathiino[3,2-b]pyridine)(η⁵-cyclopentadienyl)iron hexafluorophosphate crystalizes in the orthothombic system, space group Pbca; the dihedral angle between the planes of outer rings was found to be 176.8 (1).     

Isomerization and ring-closing metathesis for the synthesis of 6-, 7- and 8-membered benzo- and pyrido-fused N,N-, N,O- and N,S-heterocycles

An isomerization-ring-closing metathesis (RCM) strategy afforded N-substituted 4H-1,4-benzoxazines from the protected N-allyl-2-(allyloxy)anilines. In addition, RCM was used to synthesize the N-substituted, 8-membered benzo-fused heterocycles from the respective diallyl compounds: 1,2,5,6-tetrahydro-1,6-benzodiazocine, 5,6-dihydro-2H-1,6-benzoxazocine, 5,6,9,10-tetrahydropyrido[2,3-b][1,4]diazocine and 5,6-dihydro-2H-1,6-benzothiazocine 1,1-dioxide. The isomerization-RCM approach also afforded the 7-membered ring system, 2,5-dihydro-1,5-benzothiazepine 1,1-dioxide, from the protected N-allyl-2-(allylsulfonyl)aniline. Furthermore, the structure of 1,6-bis[(4-methylphenyl)sulfonyl]-1,2,5,6-tetrahydro-1,6-benzodiazocine was confirmed by a single crystal X-ray determination.     

Facile synthesis of 6,12b-diaza-dibenzo[a,h]azulen-7-ones and benzo[f]pyrrolo[1,2-a][1,4]diazepin-4-ones via CuI/l-proline catalyzed intramolecular N-arylation

Facile intramolecular N-arylation catalyzed by CuI/l-proline has been developed to prepare 6,12b-diaza-dibenzo[a,h]azulen-7-ones and benzo[f]pyrrolo[1,2-a][1,4]diazepin-4-ones in good to excellent yields.     

Tellurium in organic synthesis: X. Synthesis of 3-halogenobenzo [b] tellurophene derivatives

Several substituted 3-halogenobenzo[b] tellurophenes have been synthesized by treating phenylacetylenes with TeO₂ in acetic acid in the presence of a lithium halide. A mechanism is postulated involving an electrophilic attack by a solubilized tellurium species on the acetylenic bond with introduction of a halogen atom followed by cyclization to the benzo[b]tellurophene system. The benzo[b]tellurophenes can be easily chlorinated with Cl₂ gas to yield benzo[b]tellurophene 1,1-dichloride derivatives, but attempted lithiation is the 3-position was unsuccessful and resulted in a ring rupture. When refluxed in trifluoroacetic acid 3-chlorobenzo[b]tellurophene was converted into 3-oxo-2,3-dihydrobenzo[b]tellurophene.     

Synthesis of Some New Benzo[b][1,4]diazepine Based Heterocycles

Preparation of 4‐chloro‐3H‐benzo[b][1,4]diazepine‐2‐carbaldehyde 5 , which is used as a key intermediate in the synthesis of chalcones derivatives, via its condensation with some aromatic acetophenone derivatives under ethanol piperidine condition was described. Also illustrated was the reaction of such chalcones with available nucleophilics and reagents of active methylene group to afford new series of fused and isolated pyrazoles, isoxazolines pyrimidines, pyridines, triazolo[1,5‐a]pyrimidines, benzo[1,4]oxa(thia)zepines, and pyrido[1,2‐a]benzimidazoles incorporating 4‐chloro‐3H‐benzo[b][1,4]diazepine moiety, which have a potential pharmaceutical interest. Furthermore, condensation reaction of 4‐chloro‐3H‐benzo[b][1,4]diazepine‐2‐carbaldehyde with aromatic amine derivatives to afford the Schiff's bases was described. The C═N double bond of the latter compounds has been reacted with chloroketene to give β‐lactams and with sulfanylacetic acid to give the 2‐(4‐oxo‐1,3‐thiazolidinyl)‐substituted derivative. The structures of the newly prepared compounds were established by elemental analysis, IR, MS, and ¹H NMR spectral analysis.     

Site-specific preparation of 4-substituted-6-fluoro(carboalkoxyl)benzo[b]furans and benzo[b]thiophenes via base-catalyzed cyclization of enyne derivatives

A site-specific synthesis of 4-substituted-6-fluoro(carboalkoxyl)benzo[b]furans and benzo[b]thiophenes is described. The reactions of heterocyclic aromatic aldehydes with a Wittig reagent, followed by Sonogashira reaction with terminal alkynes, and subsequent base-catalyzed cyclization site-specifically provide 4-substituted-6-fluoro(carboalkoxyl)benzo[b]furans and benzo[b]thiophenes in good yields.     

Selective construction of indeno[1,2-b]phenothiazine and indeno[2,1-c]phenothiazine via tandem annulation reaction

AcOH promoted annulation reaction of 2-arylideneindane-1,3-diones with methyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate in refluxing ethanol afforded pentacyclic tetrahydroindeno [1,2-b]phenothiazine in satisfactory yields and with high diastereoselectivity according to the unexpected tandem annulation process. When the above reaction was carried out in refluxing acetic acid, isomeric dihydroindeno [1,2-b]phenothiazines and dihydroindeno [2,1-c]phenothiazines were obtained in comparable yields according to alternate tandem annulation process.     

A facile synthesis of (Z)-1, 6-disubstituted-7H-benzo[b][1,5]diazonin-7-one derivatives via arylation-allylation-RCM pathway of anthranilamide and isatoic anhydride

A facile and efficient method has been developed for the synthesis of (Z)-6-allyl-1-phenyl-1,2,5,6-tetrahydro-7H-benzo[b][1,5]diazonin-7-one and (Z)-1,6-diphenyl-1,2,5,6-tetrahydro-7H-benzo[b][1,5]diazonin-7-one from anthranilamide via N-arylation/N-allylation and from isatoic anhydride via ring opening/N-arylation/N-allylation followed by ring closing metathesis using Grubbs-II catalyst as a key step. Grubbs-II catalyst was found to be superior over Grubbs-I catalyst in terms of reaction time and yield of the product, and the routes developed were suitable to synthesize benzo fused nine membered nitrogen heterocycles. The requirement of diallylated substrates with protected amine and amide nitrogen is suitable for RCM has been established for the synthesis of diazoninone derivatives.     

Heck-like coupling and Pictet-Spengler reaction for the synthesis of benzothieno[3,2-c]quinolines

A series of 6-arylbenzothieno[3,2-c]quinolines were synthesised in three steps from benzo[b]thiophene. After a selective Heck-type coupling of benzo[b]thiophene with different o-nitroaryl bromides to obtain 2-(o-nitroaryl)benzo[b]thiophenes, corresponding 2-(benzo[b]thiophen-2-yl)anilines were involved in a Pictet-Spengler reaction to form the quinoline cycle.     

Microwave-assisted synthesis of novel N-(4-phenylthiazol-2-yl)-benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides inspired by marine topsentines and nortopsentines

We report the synthesis of novel N-(4-phenylthiazol-2-yl)-substituted benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides, which were inspired by marine topsentines and nortopsentines. Condensation of 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt) with various ortho-halogenated anilines, aminopyridines and aminophenols gave the corresponding aryliminodithiazoles in good to excellent yields. Copper(I)-mediated or nucleophilic-assisted cyclization of aryliminodithiazoles furnished cyano-functionalized benzo[d]thiazoles, thiazolo[4,5-b]- and thiazolo[5,4-b]-pyridines and benzo[d]oxazoles. The latter were condensed with substituted 4-phenylthiazol-2-amines to furnish twenty seven new polyaromatic carboximidamides in moderate to good yields.     

Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.