Asymmetric addition of grignard reagents to chiral 1-acylpyridinium salts: A chiral auxiliary study

Comins, Daniel L.; Guerra‐Weltzien, L.

doi:10.1016/0040-4039(96)00709-5

Cited by 43 publications

(17 citation statements)

References 16 publications

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“…75 This chiral auxiliary is often more effective than TCC derivatives due to having an isopropyl group at the cyclohexyl ring. 76 The pyridinium salt 3c with CPC was used for the synthesis of indolizidine alkaloid (+)-209D 77 and (−)-perhydrohistrionicotoxin. 78 Chiral 1,4-dihydropyridines were synthesized by the faceselective addition of nucleophiles to a pyridinium salt with a chiral auxiliary.…”

Section: Nucleophilic Additionmentioning

confidence: 99%

“…The authors developed a new chiral auxiliary (1 S ,2 R ,4 S )-2-(1-methyl-1-phenylethyl)-4-(2-propyl)-cyclohexanol, (−)-CPC 2c (Scheme ), which is prepared from limonene oxide . This chiral auxiliary is often more effective than TCC derivatives due to having an isopropyl group at the cyclohexyl ring . The pyridinium salt 3c with CPC was used for the synthesis of indolizidine alkaloid (+)-209D and (−)-perhydrohistrionicotoxin …”

Section: Reactions Involving Cationic Intermediates or Transition Statesmentioning

confidence: 99%

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Cation−π Interactions in Organic Synthesis

2018

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The cation−π interaction is an attractive noncovalent interaction between a cation and a π system. Due to the stronger interaction energy than those of the other π interactions, such as π–π and CH−π interactions, the cation−π interaction has recently been recognized as a new tool for controlling the regio- and stereoselectivities in various types of organic reactions. This review attempts to cover a variety of organic reactions controlled by cation−π interactions, which includes not only recent examples but also those reported before the term “cation−π interaction” was defined in 1990. This review will provide comprehensive knowledge on the role of cation−π interactions in organic synthesis.

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Section: Nucleophilic Additionmentioning

confidence: 99%

Section: Reactions Involving Cationic Intermediates or Transition Statesmentioning

confidence: 99%

Cation−π Interactions in Organic Synthesis

2018

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“…Our synthetic plan called for the preparation of enantiopure dihydropyridone 6 . Initially, we investigated the addition of Grignard reagent 4 to chiral 1-acylpyridinium salt 3 , which was prepared in situ from 4-methoxy-3-(triisopropylsilyl)pyridine and the chloroformate of (−)- trans -2-(α-cumyl)cyclohexanol (TCC) 12 (Scheme ). The crude dihydropyridone product 5 was reduced to give a 57% overall yield of 6 .…”

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confidence: 99%

Enantiopure N-Acyldihydropyridones as Synthetic Intermediates: Asymmetric Synthesis of (−)-Septicine and (−)-Tylophorine

1997

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A concise asymmetric synthesis of (-)-septicine (1) and (-)-tylophorine (2) was accomplished with a high degree of stereocontrol in eight and nine steps, respectively. Addition of 4-(1-butenyl)magnesium bromide to 1-acylpyridinium salt 3, prepared in situ from 4-methoxy-3-(triisopropylsilyl)pyridine and the chloroformate of (-)-trans-2-(alpha-cumyl)cyclohexanol, gave a 91% yield of diastereomerically pure dihydropyridone 7. Oxidative cleavage of 7 and subsequent reduction provided alcohol 6 in 81% yield. Conversion of 6 to the chloride followed by treatment with sodium methoxide gave indolizidinone 9 in high yield. Bromination and conjugate reduction of 9 with L-Selectride, and trapping the intermediate enolate with N-(5-chloro-2-pyridyl)triflimide, provided bromovinyl triflate 11. Palladium-catalyzed cross-coupling of excess (3,4-dimethoxyphenyl)zinc bromide and 11 gave (-)-septicine (1). On the basis of this synthesis, (-)-1 was assigned the Rconfiguration. Reaction of 1 with vanadium(V) trifluoride oxide in TFA/CH(2)Cl(2) effected oxidative coupling to give a 68% yield of (-)-tylophorine (2).

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“…With compound 11 in hand, the possibility of a corresponding asymmetric synthesis was investigated. The analogous reaction using the chiral chloroformate of (−)-CPC 19 gave octahydroquinolone 12 in an unoptimized but promising 80% yield and 50% de.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Studies toward the Synthesis of Lepadiformine A

2016

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Herein is described an original approach to access a tricyclic framework of the lepadiformine-type alkaloids. A Grignard/N-acylpyridinium salt reaction of a 4-methoxytetrahydroquinoline is the key carbon–carbon bond-forming step that was used to establish the desired absolute stereochemistry at the C2 position of the target alkaloid. The synthesis features an allylation reaction with an N-acyliminium ion to set the C10 quaternary stereocenter, a mild dissolving-metal cleavage of hindered phenyl carbamates, and an aminoiodocyclization to form the pyrrolidine ring. While this route does not provide the correct C10 stereochemistry, it showcases an efficient method to build analogues with the ring system of this class of alkaloids in 11 steps overall.

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Asymmetric addition of grignard reagents to chiral 1-acylpyridinium salts: A chiral auxiliary study

Cited by 43 publications

References 16 publications

Cation−π Interactions in Organic Synthesis

Cation−π Interactions in Organic Synthesis

Enantiopure N-Acyldihydropyridones as Synthetic Intermediates: Asymmetric Synthesis of (−)-Septicine and (−)-Tylophorine

Studies toward the Synthesis of Lepadiformine A

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