Triazole Carbene Research Articles

N-Heterocyclic Carbene/Lewis Acid Dual Catalysis for the Divergent Construction of Enantiopure Bridged Lactones and Fused Indenes.

The chiral triazole carbene and Ti(OPr-i)4 cocatalyzed reaction between α,β-unsaturated aldehydes and 2-(aroylvinyl)benzaldehydes was systematically studied. A divergence in reaction pathways was observed under different reaction conditions. In benzene solvent and at ambient temperature, the reaction produced 4,5-dihydro-1,4-methanobenzo[c]oxepin-3-ones, the bridged caprolactones, as the major products in moderate yields with excellent enantioselectivity. The same reaction in dichloroethane and at 50 °C, however, gave 2,8-dihydrocyclopenta[a]indenes as the major products in most cases. The application of the method developed was demonstrated by the transformation of the bridged lactone products into enantiopure 4-hydroxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids.

ChemInform Abstract: Chiral N‐Heterocyclic Carbene/Lewis Acid Cooperative Catalysis of the Reaction of 2‐Aroylvinylcinnamaldehydes: A Switch of the Reaction Pathway by Lewis Acid Activation.

AbstractWhile chiral triazole carbenes catalyze an intramolecular cyclization reaction of title compounds (I), a combination of triazole carbene and Ti(OiPr)4 catalyzes the intramolecular dimerization to afford indeno‐furan‐derivatives (II) with high stereoselectivities under the same reaction conditions.

Chiral N-heterocyclic carbene/Lewis acid cooperative catalysis of the reaction of 2-aroylvinylcinnamaldehydes: a switch of the reaction pathway by Lewis acid activation.

The chiral N-heterocyclic carbene/Lewis acid co-catalyzed reaction of 2-aroylvinylcinnamaldehydes produced good yields of indeno[1,2-c]furan-1-one derivatives with excellent enantioselectivity and diastereoselectivity. A switch of intramolecular cyclization to intermolecular dimerization was achieved by the cooperative catalysis of chiral triazole carbene and Ti(OPr-i)4 catalysts.

ChemInform Abstract: Changing Reaction Pathways of the Dimerization of 2‐Formylcinnamates by N‐Heterocyclic Carbene/Lewis Acid Cooperative Catalysis: An Unusual Cleavage of the Carbon—Carbon Bond.

Catalyzed by a triazole carbene, the dimerization of 2-formylcinnamates underwent benzoin condensation followed by intramolecular oxa-Michael addition to afford isochromeno[4,3-c]isochromene products. Under the catalysis of a combination of triazole carbene and Ti(OPr-i)4 catalysts, the dimerization reaction of 2-formylcinnamates proceeded through a completely different route to furnish the formation of isochromenone derivatives with the elimination of an acetate moiety.

N-heterocyclic carbene-catalyzed diastereoselective and enantioselective reaction of 2-aroylvinylcinnamaldehydes with α,β-unsaturated imines: complete control and switch of diastereoselectivity by N-substituents of catalysts.

Highly diastereoselective and enantioselective reactions between 2-aroylvinylcinnamaldehydes and α,β-unsaturated imines were achieved under asymmetric catalysis of chiral triazole carbene catalysts. In the presence of N-anisylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt, the reaction of 2-aroylvinylcinnamaldehydes with α,β-unsaturated imines afforded indeno[2,1-c]pyran-1-one derivatives 4 with 90%-99% ee, while enantiopure indenocyclopentan-1-ones 5 (>99% ee) were obtained under the catalysis of N-mesitylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt. A slight variation of an N-substituent on triazole carbenes was found to switch completely the diastereoselectivity of the reaction for the formation of indeno[2,1-c]pyran-1-ones.

Changing reaction pathways of the dimerization of 2-formylcinnamates by N-heterocyclic carbene/Lewis acid cooperative catalysis: an unusual cleavage of the carbon-carbon bond.

Catalyzed by a triazole carbene, the dimerization of 2-formylcinnamates underwent benzoin condensation followed by intramolecular oxa-Michael addition to afford isochromeno[4,3-c]isochromene products. Under the catalysis of a combination of triazole carbene and Ti(OPr-i)4 catalysts, the dimerization reaction of 2-formylcinnamates proceeded through a completely different route to furnish the formation of isochromenone derivatives with the elimination of an acetate moiety.

Changing the Reaction Pathway by NHC/Brønsted Base Cooperative Catalysis: Highly Stereoselective Synthesis of Multifunctional Benzo[a]fluoren-11-ones from the Dimerization of 2-(Aroylvinyl)arylaldehydes

The unprecedented NHC/Brønsted base-cocatalyzed dimerization reaction of 2-(aroylvinyl)arylaldehydes was reported. In the presence of a triazole carbene catalyst alone, no reaction of 2-(aroylvinyl)arylaldehydes was observed. However, the combination of triazole carbene and 4-methoxyphenolate efficiently catalyzed the dimerization of 2-(aroylvinyl)arylaldehydes to proceed through a benzoin-Michael-Michael reaction cascade, producing 6-aroyl-5-(aroylmethyl)-11a-hydroxybenzo[a]fluoren-11-ones as the sole diastereomers in good yields.

NHC Brønsted base-catalyzed transformations of isochromene derivatives: regulation of products by the structures of carbene catalysts

Two different transformations of α-(isochromen-1-yl)ketones catalyzed by NHC Brønsted bases are reported. In the presence of a triazole carbene, α-(isochromen-1-yl)ketones isomerized into β-(2-(aroylmethylene)phenyl)-α,β-unsaturated ketones in 38-88% yields, while the same reaction catalyzed by an imidazole carbene produced 1-aroylnaphthalene derivatives in 90-99% yields. This work not only provides a new method for the synthesis of a novel type of α,β-unsaturated ketone and multi-substituted naphthalene derivatives, but also advances the application of NHC catalysts in the field of Brønsted base-catalysis.

N-Heterocyclic Carbene Catalyzed Reaction of Phthalaldehydes: Controllable Stereoselective Synthesis of Polyhydroxylated Spiro- and Fused Indenones Dictated by the Structure of NHC Catalysts

The N-heterocyclic carbene catalyzed stereoselective dimerization reactions of phthalaldehydes produced polyhydroxylated spiro- or fused indenones. The reaction pathways were dictated by the structures of NHC catalysts. Under the catalysis of a imidazole carbene, phthalaldehydes produced dihydroxylspiro[indene-2,1'-isobenzofuran]-3-ones in good to excellent yields, whereas a triazole carbene catalyzed reaction of phthalaldehydes afforded fully cis-trihydroxylindeno[2,1-a]inden-5-ones in high yields. This work not only provides a highly efficient method for the construction of valuable polyhydroxyl substituted indene derivatives that are not easily assembled by other synthetic means but also reflects the versatility of organocatalysis using N-heterocyclic carbenes.

ChemInform Abstract: Synthesis of Novel Synthetic Intermediates from the Reaction of Benzimidazole and Triazole Carbenes with Ketenimines and Their Application in the Construction of Spiro‐Pyrroles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Synthesis of Novel Synthetic Intermediates from the Reaction of Benzimidazole and Triazole Carbenes with Ketenimines and Their Application in the Construction of Spiro‐Pyrroles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of novel synthetic intermediates from the reaction of benzimidazole and triazole carbenes with ketenimines and their application in the construction of spiro-pyrroles

2-(2-Alkoxycarbonyl-1-arylamino-1-propenyl)benzimidazolium and 5-(2-alkoxycarbonyl-1-arylamino-1-propenyl)triazolium salts were synthesized in good yields from the reaction of benzimidazole and triazole carbenes with ketenimines. Upon treatment with a base, both salts were converted into novel 1,3-dipoles which underwent [3+2] cycloaddition reactions with electron-deficient alkynes and allenes to produce benzimidazole-spiro-pyrroles or triazole-spiro-pyrroles. This work provides novel synthons for the construction of multifunctional spiro-pyrrole derivatives that are not easy accessible by other synthetic methods and are potentially amenable to further transformations.

Tetrazole and triazole carbene complexes of group 6 metal carbonyls

In order to study the relative stability of cis- and trans-isomers of bis(NHC)tetracarbonyl complexes of group 6 metals, we synthesized the corresponding complexes with triazolin- and tetrazolinylidene ligands. By reaction of the free carbene (L = 1,3,4-triphenyl-4,5-dihydro-1 H-1,2,4-triazolin-5-ylidene) – first synthesized by Enders – with the hexacarbonyls of Cr, Mo and W the corresponding M(L)(CO) 5 complexes are generated. Depending on an excess of carbene also the cis-(L) 2Mo(CO) 4 complex was obtained. The latter can be photolytically converted to the trans-(L) 2Mo(CO) 4 complex. The corresponding complexes with the 1,4-dimethyltetrazolin-5-ylidene ligand (L′), Cr(L′)(CO) 5, cis-(L′) 2Cr(CO) 4 and trans-(L′) 2Cr(CO) 4 can be obtained by reaction of hexacarbonyl-μ-trihydroxy-dichromate with dimethyltetrazolium salt. In the cis-(L′) 2Cr(CO) 4 complex, one carbonyl ligand can be replaced by donor ligands such as pyridine or phenylisocyanide to form sym–mer-tricarbonyl complexes. All new complexes are fully characterized by spectroscopy and most by single-crystal X-ray analysis.