STEREOSPECIFIC SYNTHESIS OF (2S,4S,6S)-2-AMINO-4,6-DIHYDROXYPIMELIC ACID

The Lewis acid catalyzed stereoselective carbonyl-ene-reaction between 5S)-1-benzoyl-2-tert-butyl-3-methyl-5-(2-propenyl) imidazolidin-4-one (2) and anhydrous butyl glyoxylate was investigated with the aim to o btain highly functionalized amino acids. This reaction is assumed to p roceed in a nonsynchronous fashion, giving rise to competing reactions within the time interval between the C-C bond formation and the proto n migration step. Thus, a hypothesized dipolar intermediate could unde rgo two reaction pathways: besides conventional ene product 3, two fur ther products 4 and 5 are obtained via nucleophilic attack involving t wo different neighboring carbamoyl groups. Acidic hydrolysis of both p roducts afforded title compound 1. The absolute configuration of the t wo newly formed chiral centers was assigned by NMR measurements of lac tone 4 and its rigid derivative 7. By varying the temperature (-20 deg rees to 25 degrees C) and the type of Lewis acid (SnCl4, FeCl3) the re action can be directed to give either of the possible reaction product s. A plausible reaction mechanism is proposed.