The Use of (-)-Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8-Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures

Julien Doulcet, G. Richard Stephenson

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The effect of organolithium reagent (RLi: R=nBu, iPr, sBu, tBu), solvent (diethyl ether, diethyl ether/THF and MTBE), and stoichiometry on the (-)-sparteine-mediated silylation of 7,8-dipropyltetrathia[7]helicene shows that, unusually, substantially more than 0.5 equivalent of RLi (R=iPr, sBu, tBu) and a large excess of (-)-sparteine (R=nBu, sBu) is often needed to achieve substantial conversions and good ee values. With nBuLi, however, just one equivalent of the organolithium reagent is sufficient to obtain high conversions. Our best results were obtained using the convenient tBuLi/(-)-sparteine adduct with which the need for a high (-)-sparteine/RLi ratio can be avoided. Single- and double-kinetic resolution (KR) procedures give enantiopure samples of 2-trimethylsilyl- and 2,13-di(trimethylsilyl)-7,8-dipropyltetrathia[7]helicene and two-step double-KR combining (-)-sparteine/sBuLi and chiral formamides affords the synthetically valuable 2-formyl-7,8-dipropyltetrathia[7]helicene. This is the first use of (-)-sparteine for the enantioselective lithiation of helicenes and the first report of tBuLi outperforming sBuLi in a (-)-sparteine-mediated procedure.
LanguageEnglish
Pages18677-18689
Number of pages13
JournalChemistry - A European Journal
Volume21
Issue number51
DOIs
Publication statusPublished - 12 Nov 2015
Externally publishedYes

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Sparteine
Kinetics
Ether
Formamides
Stoichiometry

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title = "The Use of (-)-Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8-Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures",
abstract = "The effect of organolithium reagent (RLi: R=nBu, iPr, sBu, tBu), solvent (diethyl ether, diethyl ether/THF and MTBE), and stoichiometry on the (-)-sparteine-mediated silylation of 7,8-dipropyltetrathia[7]helicene shows that, unusually, substantially more than 0.5 equivalent of RLi (R=iPr, sBu, tBu) and a large excess of (-)-sparteine (R=nBu, sBu) is often needed to achieve substantial conversions and good ee values. With nBuLi, however, just one equivalent of the organolithium reagent is sufficient to obtain high conversions. Our best results were obtained using the convenient tBuLi/(-)-sparteine adduct with which the need for a high (-)-sparteine/RLi ratio can be avoided. Single- and double-kinetic resolution (KR) procedures give enantiopure samples of 2-trimethylsilyl- and 2,13-di(trimethylsilyl)-7,8-dipropyltetrathia[7]helicene and two-step double-KR combining (-)-sparteine/sBuLi and chiral formamides affords the synthetically valuable 2-formyl-7,8-dipropyltetrathia[7]helicene. This is the first use of (-)-sparteine for the enantioselective lithiation of helicenes and the first report of tBuLi outperforming sBuLi in a (-)-sparteine-mediated procedure.",
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The Use of (-)-Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8-Dipropyltetrathia[7]helicene : Single and Double Kinetic Resolution Procedures. / Doulcet, Julien; Stephenson, G. Richard.

In: Chemistry - A European Journal, Vol. 21, No. 51, 12.11.2015, p. 18677-18689.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The Use of (-)-Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8-Dipropyltetrathia[7]helicene

T2 - Chemistry - A European Journal

AU - Doulcet, Julien

AU - Stephenson, G. Richard

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Y1 - 2015/11/12

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KW - (-)-sparteine-mediated lithiation

KW - asymmetric synthesis

KW - double-KR

KW - kinetic resolution

KW - tetrathia[7]helicenes

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SN - 0947-6539

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