Lawrence W. Nicholson

A simple and convenient synthesis of β-amino alcohol chiral auxiliaries based on limonene oxide

Abstract A series of chiral β-amino alcohols was prepared by the reaction of secondary amines with a 1:1 mixture of cis - and trans -limonene oxide in the presence of water as a catalyst. The β-amino alcohol obtained was derived from the trans -limonene oxide, and the unreacted cis -limonene oxide was recovered from the reaction mixture. The β-amino alcohols are useful chiral auxiliaries for the addition of diethylzinc to benzaldehyde.

Boranes in synthesis. 2. Asymmetric synthesis of β-amino alcohols. A facile conversion of 2-amino acetophenones to the corresponding β-amino alcohols in high enantiomeric purity

The asymmetric reduction of 2-amino acetophenones with Ipc2BH or Ipc2BCl at −78°C, yields the corresponding β-amino alcohols in good to excellent yields. Although only modest (12–45% ee) enantiomeric excesses were obtained with Ipc2BH, 75–99% enantiomeric excesses were obtained when Ipc2BCl was used as the asymmetric reducing agent.

Boranes in synthesis — VII. Synthesis of 2-dialkylamino-6,6-dimethylbicyclo[3.1.1]heptan-3-ols from (R)-(+)-nopinone. Chiral auxiliaries for the addition of diethylzinc to aromatic aldehydes

Abstract The reaction of (1 R ,5 S )-(+)-nopinone with secondary amines in cyclohexane with the azeoptropic removal of water afforded excellent yields of the correspondin enamines. Hydroboration of these enamines with BMS followed by methanolysis and oxidation with basic hydrogen peroxide gave the corresponding (1 R ,2 S ,3 S ,5 R )-2-dialkylamino-6,6-dimethylbicyclo[3.1.1]heptan-3-ols. These amino alcohols, in spite of their trans geometry, served as chiral auxiliaries for the addition of diethylzinc to aromatic aldehydes to give nearly quantitative yields of the corresponding ( R )-1-aryl-1-propanols with 52 to 80% ee.

High-performance liquid chromatographic separation of β-amino alcohols II. Separation of trans-2-(dialkylamino)cyclohexanols on an amylose-based chiral stationary phase

Direct enantiomeric separations of racemic mixtures of trans-2-(dialkylamino)cyclohexanols were achieved with a variety of alcohol-modified pentane mobile phases and a Chiralpak AD chiral stationary phase. The effects of the aliphatic component and the alcohol modifier in the mobile phase were studied independently. A variety of alcohol modifiers were investigated that introduced steric factors or affected hydrogen bonding. Ring-size effects of the substituents were noted.

Boranes in synthesis. 4. Hydroboration of enamines derived from 2-norbornanone. Synthesis of endo-3-(dialkylamino)-exo-2-norbornanols and endo-2-(dialkylamino)norbornanes

Abstract The hydroboration of the enamines derived from 2-norbornanone with BMS followed by methanolysis and oxidation with basic hydrogen peroxide afforded moderate yields of the corresponding endo-3-(dialkylamino)-exo-2-norbornanols. Hydroboration with 9-BBN followed by methanolysis gave excellent yields of the corresponding endo-2-(dialkylamino)norbornanes.