Novel synthesis of alkoxy substituted oxa[9]helicenes by the reaction of helical quinone with alcohols

The reaction of helical quinone with alcohols in the presence of Brønsted acid such as para-toluenesulfonic acid (pTSA) or HCl proceeded smoothly to produce the corresponding alkoxy substituted oxa[9]helicenes in good yields.     

Versatility of 2-oxobenzo[h]chromene for the synthesis of oxabenzo[c]chrysenes

An innovative and concise synthesis of (7,8-dihydro-5-oxabenzo[c]chrysene-6-ylidene)acetonitriles is described through base catalyzed ring transformation of 2-oxo-4-piperidin-1-yl-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with 1-tetralone in very good yields.     

A new approach to helical primary structures of four-membered rings: (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane

A new approach to helical primary structures of four-membered rings uses a cycloaddition of a trimethylenketeniminium salt to suitable tailored methylenecyclobutanes to assemble the desired carbon framework. The results are short and effective syntheses of (M)-trispiro[3.0.0.3.2.2]tridecane [(M)-5], and (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane [(P)- and (M)-24]. Unlike helices of three-membered rings, the specific rotation decreases, as the length of the helix increases.     

A synthesis of dihydroimidazo[5,1-a]isoquinolines using a sequential Ugi-Bischler-Napieralski reaction sequence

A flexible route to analogues of dihydroimidazo[5,1-a]isoquinolines is described. The synthesis hinges on a sequential Ugi coupling, followed by a Bischler-Napieralski reaction to form the imidazole isoquinoline core. This route facilitates the introduction of a range of substitutions throughout the carbon framework.     

Pd-Cu catalyzed heterocyclization during Sonogashira coupling: synthesis of 2-benzylimidazo[1,2-a]pyridine

The reaction of 2-amino-1-(2-propynyl)pyridinium bromide with various iodobenzenes, catalyzed by Pd-Cu, leads to the formation of 2-benzylimidazo[1,2-a]pyridines.     

Synthesis of N-substituted benzo[c][1,7]- and benzo[c][1,8] phenanthrolin-(5H)-6-ones through a Pd-mediated Suzuki-Miyaura heteroaryl-aryl coupling reaction

In the course of the search for non-camptothecin topoisomerase I inhibitors we have undertaken the synthesis of N-substituted benzo[c][1,7]- and benzo[c][1,8]phenanthrolinone derivatives. An intermolecular Suzuki-Miyaura heteroaryl-aryl coupling reaction was planned as the key step. Then a nitro reduction followed by a concomitant lactamization achieved the construction of the tetracycle structures. This methodology permitted a rapid and efficient elaboration of biologically potent compounds.     

A concise synthesis of novel naphtho[a]carbazoles and benzo[c]carbazoles

Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps include the use of the Suzuki-Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted aromatic ring-forming reaction.     

Novel synthesis of oxa[9]helicenes by Lawesson’s reagent-mediated cyclization of helical quinone derivatives

New oxa[9]helicenes which possess one furan ring have been readily prepared by reactive helical quinone with Lawesson’s reagent or phosphorus pentasulfide in good yields. The versatility of this protocol has been demonstrated with various substituted helical quinones.     

Novel synthesis of pyridazino[4,5-b][1,4]oxazin-3,8-diones

A novel and effective synthesis of pyridazino[4,5-b][1,4]oxazin-3,8-diones via Smiles rearrangement is presented. Treatment of N-substituted 2-chloro(or hydroxy)acetamide, 2-tetrahydropyranyl-4-chloro-5-hydroxy(or chloro)pyridazin-3-one and cesium carbonate in refluxing acetonitrile was afforded the corresponding pyridazino[4,5-b][1,4]oxazin-3,8-diones in excellent yield.     

An unexpected rearrangement of 3-unsubstituted-2-acyl substituted indole phenylhydrazones. A new method for benz[c]β-carboline synthesis

A new type of rearrangement of 3-unsubstituted-2-acyl substituted indole phenylhydrazones with formation of a quinoline ring under acid catalysed conditions was observed.     

Regioselective synthesis of 6-benzylthiazolo[3,2-b]1,2,4-triazoles during Sonogashira coupling

The reaction of 3-mercaptopropargyl-1,2,4-triazoles with various iodobenzenes catalyzed by Pd-Cu leads to the regioselective formation of 6-benzylthiazolo[3,2-b]1,2,4-triazoles 4. The structure of 4d was confirmed by X-ray analysis.     

An efficient phosphine-free palladium coupling for the synthesis of new 2-arylbenzo[b]thiophenes

Straightforward and rapid access to 2-arylbenzo[b]thiophenes has been developed. It involved a catalytic coupling of 3-activated benzo[b]thiophenes with several aryl halides in the presence of a phosphine-free palladium system. In case of fragile functional groups such as aldehydes, a quaternary ammonium was used as an additive as with the other substrates, the coupling performed better and faster in the presence of a crown ether, the best one being DCH-18-C-6, with good yields and low reaction times. This method would provide a direct access to novel structures of biological interest.     

Domino synthesis of 2-arylbenzo[b]furans by copper(II)-catalyzed coupling of o-iodophenols and aryl acetylenes

A wide range of 2-arylbenzo[b]furans are synthesized through domino intermolecular C_(aryl)-C_(alkynyl) bond formation followed by intramolecular C_(alkynyl)-O bond forming cyclization via copper(II)-catalyzed coupling of o-iodophenols and aryl terminal acetylenes. This method requires neither expensive palladium catalyst nor oxophilic phosphine ligands, can tolerate different functional groups. The methodology is successfully utilized in formal synthesis of β-amyloid aggregation inhibitor 5-chloro-3-[4-(3-diethylaminopropoxy)benzoyl]-2-(4-methoxyphenyl) benzofuran.     

Tandem synthesis of functionalized tetrahydro-4aH-benzo[c]isoquino[1,2-t]pyrrolo[1,2-a][1,6]naphthyridines

An effective route to fused hexacyclic derivatives of isoquinoline is described via tandem reaction of isoquinoline, dialkyl acetylenedicarboxylates, and 3-chloropentane-2,4-dione or alkyl 3-chloroacetoacetates.     

Novel synthesis of benzo[b]carbazoles

A new method was adopted for the synthesis of benzo[b]carbazoles by Claisen condensation followed by Fischer indole cyclization. Newly synthesized benzo[b]carbazoles were treated with ethanol amine in the presence of polyphosphoric acid which leads to the formation of pyrazino carbazoles. All the synthesized compounds were characterized by all spectral means.     

Stereoselective synthesis of spirocyclic oxindoles based on a one-pot Ullmann coupling/Claisen rearrangement and its application to the synthesis of a hexahydropyrrolo[2,3-b]indole alkaloid

An efficient and convenient approach to the synthesis of spirocyclic oxindoles from iodoindoles has been developed. The most striking feature of this approach is that the sequential intramolecular Ullmann coupling and Claisen rearrangement proceeds in a one-pot manner to afford 3-spiro-2-oxindoles in good yield with excellent diastereoselectivity. Application of this one-pot reaction to chiral non-racemic tertiary alcohol substrates resulted in complete chirality transfer to the spirocyclic quaternary carbon. Using this method, asymmetric total synthesis of (−)-debromoflustramine B was accomplished.     

Smiles rearrangement for the synthesis of 5-amino-substituted [1]benzothieno[2,3-b]pyridine

The Smiles rearrangement was successfully applied to 4-hydroxybenzo[b]thiophene furnishing a facile entry to the 4-amino derivative. The rearrangement was extended to 5-methoxy-4-methoxycarbonyl[1]benzothieno[2,3-b]pyridine obtained via aza-Wittig/electrocyclization reaction of novel N-(4-methoxybenzothiophen-2-yl)iminomethyldiphenylphosphorane with methyl trans-4-oxo-2-pentenoate. The preparation of a novel 5-amino-4-methoxycarbonyl[1]benzothieno[2,3-b]pyridine, which is of interest as a potential secondary peptide structure mimic, was successfully achieved.     

Facile synthesis and coupling of 3,9-dibromo-6-aryl-5H-dibenzo[d,f][1,3]diazepine derivatives

A route has been developed to prepare 3,9-dibromo-6-aryl-5H-dibenzo[d,f][1,3]diazepine derivatives which undergo facile Suzuki coupling to generate extended conjugated moieties bearing this unit. Single crystal X-ray studies on three of the coupled products provide valuable information on the conformation and bulk packing of these materials.     

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.     

Synthesis and characterization of 9,9-dialkylfluorene capped benzo[c]thiophene/benzo[c]selenophene analogs as potential OLEDs

The synthesis of soluble benzo[c]thiophene analogs capped with 9,9-dialkylfluorene at one end is described.