Regioselective synthesis of β-ketoesters from lithium enolates and methyl cyanoformate

Mander, Lewis N.; SETHI, S. P.

doi:10.1016/s0040-4039(00)87886-7

Cited by 335 publications

(198 citation statements)

References 20 publications

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“…5 We eventually discovered that the aniline nitrogen could be selectively masked by reaction of the lithium salt of aniline 15 with Mander's reagent. 11 The optimum condition identified involved dropwise addition of 3 equiv of lithium bis(trimethylsilyl)amide (LHMDS) to a THF solution of aminocyclohexenone 15 and excess methyl cyanoformate at −78 °C, in which case crystalline carbamate 16 was formed in 89% yield. When 1.5 or 2.0 equiv of LHMDS was used, significant amounts of cyclohexenone 15 were recovered.…”

Section: Enantioselective Formation Of the 34-dihydro-9a4a-(iminoetmentioning

confidence: 99%

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck−Iminium Ion Cyclization

et al. 2008

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A 1,2,3,4-tetrahydro-9a,4a-(iminoethano)-9H-carbazole (4) is a central structural feature of the Strychnos alkaloid minfiensine (1) and akuammiline alkaloids such as vincorine (5) and echitamine (6). A cascade catalytic asymmetric Heck-iminium cyclization was developed that rapidly provides 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazoles in high enantiomeric purity. Two sequences were developed for advancing 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazole 27 to (+)-minfiensine. In our first-generation approach, a reductive Heck cyclization was employed to form the fifth ring of (+)-minfiensine. In a second more concise total synthesis, an intramolecular palladium-catalyzed ketone enolate vinyl iodide coupling was employed to construct the final ring of (+)-minfiensine. This second-generation total synthesis of enantiopure (+)-minfiensine was accomplished in 6.5% overall yield and 15 steps from 1,2-cyclohexanedione and anisidine 13. A distinctive feature of this sequence is the use of palladium-catalyzed reactions to form all carboncarbon bonds in the transformation of these simple precursors to (+)-minfiensine.

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Section: Enantioselective Formation Of the 34-dihydro-9a4a-(iminoetmentioning

confidence: 99%

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck−Iminium Ion Cyclization

et al. 2008

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“…38 In four additional steps, intermediate 22 was elaborated to the Heck-cyclization precursor 23. Alkoxycarbonylation of the lithium enolate of 22 with benzyl cyanoformate 39 furnished the corresponding -keto ester, which exists as a mixture of keto and enol tautomers. Finding conditions for the reliable and efficient conversion of this intermediate to the corresponding vinyl triflate proved surprisingly difficult.…”

Section: Assembling the Heck Cyclization Precursormentioning

confidence: 99%

Enantioselective Total Synthesis of Guanacastepene N Using an Uncommon 7‐Endo Heck Cyclization as a Pivotal Step.

et al. 2007

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A convergent, enantioselective total synthesis of (+)-guanacastepene N was developed that features a 7-endo Heck cyclization as the key step. In the course of this synthesis, short syntheses of the enantiomerically pure cyclopentenone and cyclohexene building blocks 5 and 6, which constitute A and C ring fragments of guanacastepene N, were developed. These fragments were linked by a challenging conjugate addition reaction that also generated the C11 quaternary carbon stereocenter. Regioselective 7-endo Heck cyclization gave rise to a tricyclic intermediate, which was elaborated to complete the first total synthesis of guanacastepene N and the second enantioselective total synthesis of a guanacastepene natural product.

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“…Since silyl enol ethers may regioselectively be synthesized from the corresponding ketones 5) , the two-step sequence according to eq. (1) represents a useful alternative for the generation of ß-oxo esters from ketones, which has previously been carried out under strongly basic conditions using dialkyl carbonates 6) , dialkyl Oxalates 7) , methyl methoxymagnesium carbonate 8) , or methyl cyanoformate 9) . (1.5 equiv.)…”

Section: Querverweise/cross Referencesmentioning

confidence: 99%

Notizen/Notes Synthesis of β‐Oxo Esters from Silyl Enol Ethers and Dichlorobis(phenoxy)methane

1990

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Regioselective synthesis of β-ketoesters from lithium enolates and methyl cyanoformate

Cited by 335 publications

References 20 publications

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck−Iminium Ion Cyclization

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck−Iminium Ion Cyclization

Enantioselective Total Synthesis of Guanacastepene N Using an Uncommon 7‐Endo Heck Cyclization as a Pivotal Step.

Notizen/Notes Synthesis of β‐Oxo Esters from Silyl Enol Ethers and Dichlorobis(phenoxy)methane

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