ChemInform Abstract: Stereochemistry of Enantioselective Deprotonation of 4-Substituted Cyclohexanones by Chiral Bidentate Lithium Amides.

ChemInform ◽  
2010 ◽  
Vol 28 (17) ◽  
pp. no-no
Author(s):  
M. TORIYAMA ◽  
K. SUGASAWA ◽  
M. SHINDO ◽  
N. TOKUTAKE ◽  
K. KOGA
Keyword(s):  
Lithium Amides ◽  
Enantioselective Deprotonation

1,3-Dioxan-5-ones: synthesis, deprotonation, and reactions of their lithium enolates

1995 ◽  
Vol 73 (10) ◽  
pp. 1616-1626 ◽  
Author(s):  
Marek Majewski ◽  
D. Mark Gleave ◽  
Pawel Nowak
Keyword(s):  
Enantiomeric Excess ◽  
Addition Reactions ◽  
Synthetic Route ◽  
Enol Ethers ◽  
Lithium Amide ◽  
Silyl Enol Ethers ◽  
Lithium Amides ◽  
Alkyl Groups ◽  
Lithium Enolates ◽  
Enantioselective Deprotonation

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.

Enantioselective ring opening of tropinone. A new entry into tropane alkaloids

1997 ◽  
Vol 75 (6) ◽  
pp. 754-761 ◽  
Author(s):  
Marek Majewski ◽  
Ryszard Lazny ◽  
Agnieszka Ulaczyk
Keyword(s):  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Tropane Alkaloids ◽  
Amine Hydrochloride ◽  
Lithium Amides ◽  
Ring Opening Reaction ◽  
Alkyl Chloroformates ◽  
Optically Pure ◽  
Enantioselective Deprotonation

The lithium enolate of tropinone reacts with alkyl chloroformates to give 6-N-carboalkoxy-N-methyl-2-cycloheptenones (4). These compounds can be produced enantioselectively, in up to 95% ee, if chiral lithium amides (derived from optically pure amines 5–7) are used for deprotonation of tropinone in the presence of additives. The effect of additives such as LiCl, LiBr, LiF, LiClO4, CeCl3, ZnCl2, LiOH, TMEDA, HMPA, and DMPU on enantioselectivity of this deprotonation–ring opening sequence varies from slight to very large depending on the chiral amide – additive combination. Especially large increases in enantioselectivity are observed when the chiral, C2 symmetrical, lithium bis-α,α′-methylbenzylamide (Li-5a) is used with one equivalent of LiCl. This reagent is best generated in situ from the corresponding amine hydrochloride and n-BuLi (2 equiv.). The ring-opening reaction combined with transposition of the carbonyl group (via Wharton reaction or allylic oxidation) provides a new method of stereoselective synthesis of tropane alkaloids having a protected hydroxyl at C-6 or C-7 (6β- and 7β-acetoxytropanes 14a, b) and physoperuvine (19). Keywords: enantioselective deprotonation, tropane alkaloids.

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