Anthracyclinones. Enantioselective synthesis of 9-alkyanthracyclinone via highly diastereocontrolled alkylation of 4-cyanofuranosugars

Cousson, A.; Gouadec, G. Le; Monneret, Claude; Florent, Jean‐Claude

doi:10.1039/c39930000388

Cited by 11 publications

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“…Lastly, a potential liability for these two approaches is the generation of a nucleophilic acyl anion equivalent under strongly basic con-ditions. To increase the effectiveness in natural product synthesis, [26][27][28][29][30][31] an alternative is desirable to directly form the a-hydroxyketones without the need for strong base, or further unmasking of the carbonyl functionality.…”

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Thieme Chemistry Journal Awardees- Where are They Now? Intermolecular Cross-Acyloin Reactions by Fluoride-Promoted Additions of O-Silyl Thiazolium Carbinols

Mathies¹,

Mattson²,

Scheidt³

2009

Synlett

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The addition of acyl anion equivalents to aliphatic aldehydes (crossed-acyloin reaction) has been developed. Cesium fluoride with isopropanol as solvent promotes the addition of O-silyl thiazolium carbinols to various aliphatic aldehydes in moderate to good yields. These reactions represent a general procedure for the selective coupling of aliphatic aldehydes by an acyl anion reaction which have been problematic until now. Keywords acyloin reaction; carbinols; cesium fluoride; acyl anions; thiazoliumThe construction of carbon-carbon bonds through inverse reactivity patterns, or Umpolung, fuels potential strategies for the syntheses of biologically active molecules. 1,2 The benzoin 3-7 and Stetter reactions [8][9][10][11][12] are two transformations that utilize the in situ generation of acyl anion equivalents for the formation of new C-C bonds. The acyloin reaction is related to the benzoin condensation and entails the addition of an acyl anion to an aliphatic aldehyde. This process is another potentially useful Umpolung transformation that allows for direct formation of α-hydroxy ketones, a useful motif in organic chemistry.While there are reports describing catalytic intramolecular additions of aldehydes to ketones, 13,14 the literature has very few examples of successful cross-acyloin reactions in which both reactive components are aliphatic aldehydes (Scheme 1, R 1 , R 2 = alkyl). [15][16][17][18][19] To the best of our knowledge, there is only one example of a selective cross-acyloin reaction of this type reported by Johnson which involves an acylsilane and cyanide as a catalyst. 20 Alternatively, the deprotonation of protected cyanohydrins 21,22 or dithianes [23][24][25] with strong bases (e.g., LDA, n-BuLi) has generated acyl anion equivalent as suitable nucleophiles with aldehyde acceptors. While the cyanohydrin strategy can be an effective acyl anion equivalent, the liberation of cyanide to generate a ketone renders the use of cyanohydrins undesirable. Additionally, the use of cyanohydrins and dithianes as acyl anion equivalents requires a further deprotection step after completion of the key carbon-carbon bond-forming process. Lastly, a potential liability for these two approaches is the generation of a nucleophilic acyl anion equivalent under strongly basic conditions. To increase the effectiveness in natural product synthesis, 26-31 an alternative is desirable to directly form the α-hydroxyketones without the need for strong base, or further unmasking of the carbonyl functionality.In our investigations aimed at developing new unconventional nucleophiles, we have discovered that the combination of azolium salts and acylsilanes generates unique acyl anion Fax +1(847)4672184; scheidt@northwestern.edu. NIH Public Access Author ManuscriptSynlett. Author manuscript; available in PMC 2010 December 1. equivalents for additions to electrophiles, including α,α-unsaturated ketones (sila-Stetter reaction) and N-diphenylphosphinoyl imines.32 -34 However, use of these N-heterocyclic carbene (NHC) catalysts...

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