A short synthesis of koniamborine, a naturally occurring pyrano[3,2-b]indole

An expedient synthesis of the alkaloid koniamborine, the only to date isolated naturally occurring pyrano[3,2-b]indole is presented. The key pyrano[3,2-b]indole forming step is a palladium-catalyzed reductive N-heteroannulation of 2-(4-methoxy-2-nitrophenyl)-(4H)-pyrane-4-one.     

A regioselective synthesis of dispiro[oxindole-cyclohexanone]pyrrolidines and dispiro[oxindole-hexahydroindazole]pyrrolidines by sequential 1,3-dipolar cycloaddition and annulation through a microwave induced solvent-free approach

The 1,3-dipolar cycloaddition of an azomethine ylide, generated from isatin and benzylamine by a 1,5-prototopic shift route with various p-substituted 2,6-bis(arylmethylidene)cyclohexanones under different conditions, proceeded regioselectively to give novel dispiroheterocycles. The product on subsequent annulation with hydrazine hydrate afforded 4-aryl-5-phenyl(spiro[2.3″]oxindole)3′-aryl-3′,3a′,4′,5′,6′,7′-hexahydro-2H-indazolospiro[7′.3]pyrrolidines in good yield.     

Rhodium-catalyzed CH activation/cyclization of enaminones with sulfoxonium ylides toward polysubstituted naphthalenes

A rhodium-catalyzed ortho-CH functionalization and annulation between enaminones and sulfoxonium ylides was developed, affording a series of multi-substituted naphthalenes in good to moderate yields with excellent functional group compatibility. The procedure featured with enaminone acting as both a directing and cyclization bifunctional group, and the application of sulfoxonium ylide in CH functionalization.     

Towards EPC-syntheses of the structural class of cochleamycins and macquarimicins. Part 2: EPC-synthesis of the hydrindene subunit of the macquarimicins

The EPC-synthesis of the cis-hydrindene subunit of the macquarimicins, antibiotics with antitumour and anti-inflammatory activity, has been achieved. Desymmetrization of cis-1,4-cyclopent-2-enediol was succeeded by Diels-Alder reaction and functional group transformations to a tricyclic ketone. Regio- and stereoselective methylation via Claisen condensation and hydrogenation was followed by nucleophilic, intramolecular addition, reduction and acidic fragmentation. Further functional group transformations led to the target molecule.     

Synthesis of triphenylene derivatives by Pd-catalyzed Suzuki coupling/intramolecular CH activation between arylboronic acids and dibromobiphenyls

An efficient and regioselective synthesis of functionalized triphenylenes via palladium-catalyzed Suzuki-Miyaura coupling and subsequent intramolecular CH activation between arylboronic acids and dibromobiphenyls was developed. This methodology showed excellent atomic economy and regiospecificity as well as synthetic feasibility of unsymmetrical triphenylenes.     

Synthesis of fused indoles by sequential palladium-catalyzed Heck reaction and N-heteroannulation

A route to 3,4-fused indoles via two consecutive palladium-catalyzed reactions; an intramolecular Heck reaction followed by a reductive N-heteroannulation is described. Using this route, a number of indoles have been prepared having a variety of ring sizes anchored to the 3- and 4-position of the indole nucleus. Furthermore, a number of functional groups, both carbon and heteroatom substituents can be introduced in (and on) the additional ring without any detrimental effects on the two reactions.     

A simple,efficient, regioselective and one-pot preparation of N-hydroxy- and N–O-protected hydroxyindoles via cycloaddition of nitrosoarenes with alkynes. Synthetic scope,applications and novel by-products

The thermal reaction between nitrosoarenes and alkynes under alkylating conditions produces N-alkoxyindoles as the major products in moderate to good yields and excellent regioselectivity. Various electrophiles are used affording different N–O-protected hydroxyindoles in a multi-component fashion. Privileged acetylenic substrates used in reactions with substituted nitrosoarenes are arylalkynes or propiolates. Potentially bioactive compounds and other classes of highly functionalizable indole products were prepared. Reactions between o-carbomethoxy-nitrosoarenes and arylacetylenes provided tricyclic compounds containing an acylaziridine indoline skeleton.     

N-heterocyclic carbene-mediated formal [3+3] annulation of isatin-derived α, β-unsaturated acids: Access to functionalized 3,4′-spirooxindole δ-lactones

An in situ activation of isatin-derived α,β-unsaturated acids 2 for the generation of isatin-derived α,β-unsaturated acyl azoliums II was described. The acyl azoliums II were successfully applied to undergo a formal [3 + 3] annulation with 1,3-dicarbonyl compounds to access functionalized 3,4′-spirooxindole δ-lactones 4. A scale-up synthesis and an enantioselective variant of this protocol were also investigated. The stable and easily prepared acids 2 may be further utilized as promising versatile electrophilic 1,3-synthons for divergent synthesis of spirooxindoles.     

Base mediated synthesis of α-aminated aroyl/acetylnaphthalenes through [4+2] annulations

We have developed a base promoted simple, efficient and alternative approach for the synthesis of 4-amino-3-aroyl//heteroaroyl/acetyl-2-methylsulfanyl-naphthalene-1-carbonitriles by reaction of easily accessible 3,3-bis(methylthio)-1-aryl/heteroaryl/acetylprop-2-en-1-one and 2-cyanomethyl-benzonitrile. Reaction of 1-(2-halo/methoxy-phenyl)-3,3-bis(methylthio)prop-2-en-1-one and 2-cyanomethyl-benzonitrile under basic conditions also afforded 6-(methylthio)-7-oxo-7,12-dihydrobenzo[c]acridine-5-carbonitrile along with usual product. Structure of the synthesized product has been confirmed by single X-ray crystallography.     

Isoquinoline skeleton synthesis via chelation-assisted C−H activation

Transition-metal-catalyzed isoquinoline synthesis that profits from the strategy of chelation-assisted C−H activation has flourished over the past decade. By virtue of the directed C−H bond cleavage of imines, amines, amidines, oximes, hydroximoyl halides, hydrazones, or azines, diverse isoquinoline derivatives have been accessed from alkynes, conjugated dienes, or diazo compounds under the catalysis of rhodium, ruthenium, palladium, nickel, or manganese. This digest summarizes the annulation reactions via chelation-assisted C−H activation leading to isoquinolines, isoquinolinium salts, or isoquinoline N-oxides.