Stephen Belmont

• Senior Researcher at Albemarle

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Enantioselective total syntheses of indolizidine alkaloids (-)-205A and (-)-235B are described. The syntheses proceed via a common late-stage intermediate, alpha-aminonitrile 1. Absolute stereochemical control over the C8 and C8a stereocenters in these materials was achieved by a stereoselective crotylation reaction between chiral acyliminium ion (...

The cyclic anhydrides (I) are coupled with the chiral phenethylamines (II) to produce the imides (III).

Enantioselective total syntheses of the indolizidine alkaloids 167B and 209D are described. The syntheses proceed via a common late-stage intermediate, amino nitrile 8. Each alkaloid was prepared in 10 steps and approximately 23% overall yield from (S)-(-)-α-phenethylamine. The configurations of these materials were determined by a combination of o...

(S)-(-)-α-Phenethylamine (3), (S)-(-)-1-(2-chlorophenyl)ethylamine (4), (S)-(-)-1-(2,6-dichlorophenyl)ethylamine (5), and (S)-(-)-1-(2,3,4,5,6-pentachlorophenyl)ethylamine (6) have been incorporated into acyliminium ions of structural type 1 and 2. Five-membered ring acyliminium ion 1d and six-membered ring acyliminium ion 2c react with allyltrimet...

The benzaldehydes (I) are coupled with S-tert-butyl bromothioloacetate (II) in the presence of dicyclopentadienylboron triflate and diisopropylethylamine to form the anti-α-bromo-β-hydroxythiocarboxylates (III).

Trans-disubstituted glycidic esters have been prepared stereospecifically by reaction of the dicyclopentylboryl enolate of α-bromo-t-butylthioacetate with aromatic aldehydes.

Phosphole (I) adds gaseous HCl at the Patom and is transformed to give (III) via a [l,5] proton shift.

Addition to phospholes of gaseous HCI at –90 °C or of an excess of trifluoromethanesulphonic acid at –70 °C, results in P-protonation. The triflate solutions are stable up to room temperature, but the 1H-phospholium chlorides form PV adducts at –70 °C, which rapidly rearrange by a [1,5]sigmatropic H-shift. The observed product is a 1-chloro-2,5-dih...