(−)-β-Pinene-Derived N-Heterocyclic Carbenes: Application to Highly Enantioselective Intramolecular Stetter Reaction

Rafiński, Zbigniew; Kozakiewicz, Anna; Rafińska, Katarzyna

doi:10.1021/cs500207d

Cited by 54 publications

(35 citation statements)

References 67 publications

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“…98 A β-pinene-derived triazolium catalyst A 23 , reported by Rafinski, has also proven efficient for the intramolecular Stetter reaction (Scheme 35). 99 …”

Section: Umpolung Acyl-anion Catalysismentioning

confidence: 99%

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

et al. 2015

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“…98 A β-pinene-derived triazolium catalyst A 23 , reported by Rafinski, has also proven efficient for the intramolecular Stetter reaction (Scheme 35). 99 …”

Section: Umpolung Acyl-anion Catalysismentioning

confidence: 99%

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

et al. 2015

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“…All other reagents were purchased from commercial suppliers. Salicylaldehyde-derived substrates 9a-l were prepared according to the known procedures [36]. The spectra of NMR and HPLC is in the Supplementary Materials.…”

Section: General Informationmentioning

confidence: 99%

“…Those catalysts from a readily available chiral source proved to be highly effective and stereoselective in the synthesis of various chiral compounds [31][32][33][34][35]. With our ongoing interest in the development of new N-heterocyclic carbene catalysts, especially from those readily available natural chiral sources [36][37][38][39][40], we envisioned that verbenone might be an efficient chiral scaffold for N-heterocyclic carbene catalysts. Herein, we report our studies on the synthesis of novel chiral triazolium salts from (−)-verbenone and their application to the asymmetric catalytic intramolecular Stetter reaction.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of (−)-Verbenone-Derived Triazolium Salts and Their Application in Enantioselective Intramolecular Stetter Reaction

Rafiński

Krzemiński

2019

Catalysts

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Two novel chiral verbenone-derived triazolium salts have been synthesized from readily available (−)-verbenone and found to be efficient for the enantioselective intramolecular Stetter reaction. The approach, based on the intramolecular annulation between acyl anion equivalents and Michael acceptors, benefits from broad substrate scope, high chemical and stereochemical efficiency, and operational simplicity. Mono-, and disubstituded chromanone derivatives have been obtained in excellent yields and in a highly stereochemical manner.Catalysts 2019, 9, 117 2 of 12 ketooxime 4 in 87% yield by treatment with isoamyl nitrite. Due to the fact, that verbenone is not commercially available in an enantiomerically pure form, attempts of enantiomeric enrichment through crystallization at the ketoxime stage failed. Hence, we decided to reduce the carbonyl group by treatment of 4 with sodium borohydride in ethanol. Gratifyingly, crystallization of the crude 5 gave the enantiomerically pure hydroxyoxime 5 in 99% ee. Stereoselective reduction of 5 with lithium aluminium hydride afforded the amino alcohol 6 in 63% yield, which was immediately used to the next step without further purification. The lactam 8 was prepared by previously reported two-step procedure involving the formation of chloroamide 7, followed by the cyclization reaction with the use of potassium tert-butoxide. Finally, a one-pot procedure was used for the three-step conversion into triazolium salts 1A-B. The NHC precatalyst 1B could be easily and cleanly isolated as a tetraphenyl borate salt. For the salt 1A, preparation does not require chromatographic purification. Evaporation of the solvent followed by washing with diethyl ether provided a pure product that was air-and water-stable solid.

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“…Stereoselective reduction of 5 with lithium aluminum hydride afforded unsubstituted amino alcohol 6 in 76 % yield. Lactam 8 was prepared by a previously reported two‐step procedure involving the formation of chloroamide 7 , followed by an annulation reaction . Homologous triazolium salts 9 a–c were then prepared by following the procedures developed by Rovis (path A) and Bode (path B, Scheme ) .…”

Section: Figurementioning

confidence: 99%

Novel (−)‐β‐Pinene‐Derived Triazolium Salts: Synthesis and Application in the Asymmetric Stetter Reaction

Rafiński

2016

ChemCatChem

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A series of novel chiral triazolium salts derived from (−)‐β‐pinene were synthesized and found to be highly efficient precatalysts for the enantioselective intramolecular Stetter reaction. The triazolium salts prepared from a single precursor, (−)‐β‐pinene, react with antipodal enantiofacial selectivity in the Stetter reaction to afford mono‐, di‐, and trisubstituted chromanones in excellent yields with excellent stereoselectivity.

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(−)-β-Pinene-Derived N-Heterocyclic Carbenes: Application to Highly Enantioselective Intramolecular Stetter Reaction

Cited by 54 publications

References 67 publications

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

Synthesis of (−)-Verbenone-Derived Triazolium Salts and Their Application in Enantioselective Intramolecular Stetter Reaction

Novel (−)‐β‐Pinene‐Derived Triazolium Salts: Synthesis and Application in the Asymmetric Stetter Reaction

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