ChemInform Abstract: Enantioselective Deprotonation by Chiral Lithium Amide Bases: Asymmetric Synthesis of Trimethylsilyl Enol Ethers from 4-Alkylcyclohexanones.

A general synthetic route to 2-alkyl- and 2,2-dialkyl-1,3-dioxan-5-ones, using tris(hydroxymethyl)-nitromethane as the starting material, is described. Deprotonation of these compounds was studied. It was established that these dioxanones could be deprotonated with LDA; however, the reduction of the carbonyl group via a hydride transfer from LDA, giving the corresponding dioxanols, often competed with deprotonation. The reduction could be minimized by using Corey's internal quench procedure to form silyl enol ethers and was less pronounced in 2,2-dialkyldioxanones (ketals) than in 2-alkyldioxanones (acetals). Self-aldol products were observed when dioxanone lithium enolates were quenched with H2O. Addition reactions of lithium enolates of dioxanones to aldehydes were threo-selective as predicted by the Zimmerman–Traxler model. Dioxanones having two different alkyl groups at the 2-position were deprotonated enantioselectively by chiral lithium amide bases with enantiomeric excess (ee) of up to 70%. Keywords: 1,3-dioxan-5-ones, enantioselective deprotonation, chiral lithium amides.

Download Full-text

ChemInform Abstract: Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium-Amide Bases.

ChemInform ◽

10.1002/chin.200101046 ◽

2001 ◽

Vol 32 (1) ◽

pp. no-no

Author(s):

Sandrine Pache ◽

Candice Botuha ◽

Roberto Franz ◽

E. Peter Kuendig ◽

Jacques Einhorn

Keyword(s):

Asymmetric Synthesis ◽

Lithium Amide ◽

Conformationally Constrained ◽

Enantioselective Deprotonation ◽

Tricarbonylchromium Complexes

Download Full-text

Studies directed toward the synthesis of reiswigin A: Total synthesis of (±)-epi-reiswigin A

Canadian Journal of Chemistry ◽

10.1139/v03-210 ◽

2004 ◽

Vol 82 (2) ◽

pp. 333-343 ◽

Cited By ~ 7

Author(s):

David I MaGee ◽

Dean E Shannon

Keyword(s):

Total Synthesis ◽

Asymmetric Synthesis ◽

Natural Product ◽

Antiviral Agent ◽

Parallel Synthesis ◽

Practical Application ◽

Racemic Compound ◽

Lithium Amide ◽

Testing Ground ◽

Enantioselective Deprotonation

As a testing ground for the practical application of asymmetric synthesis, ()-reiswigin A, a potent antiviral agent, was chosen as a target for total synthesis. Initial studies were undertaken to prove the viability of the key asymmetric step, enantioselective deprotonation of an intermediate meso-bicyclic ketone, using a chiral lithium amide base. Enantiomeric excesses in the range of 90%94% were routinely obtained, even on runs as large as 10 g. Unfortunately, conversion of this key enantio-enriched intermediate to the natural product proved unsuccessful. While these studies were enroute, a parallel synthesis using the racemic compound was transformed into (±)-epi-reiswigin A.Key words: asymmetric deprotonation, synthesis, (±)-epi-reiswigin A.

Download Full-text