Hydrogen Bromide → 1-[2(R)-[1(R)-carboxy-2-(3,4,4-trimethyl-2,5-dioxo-1-imidazolidinyl)ethyl]-3-cyclopentylpropionyl)piperdine

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Reaction Steps

A solution of 15.11 g of the 9:1 mixture from Example 4 in 15 ml of acetic acid was treated at 0° with 15 ml of 33% hydrogen bromide in acetic acid and stirred at 0° for 4 hrs. The solution was diluted with methylene chloride, washed with water and the organic phase was dried, filtered and evaporated. The residue was crystallized from 26 ml of tert-butyl methyl ether and 26 ml of hexane, after which 6.90 g (70%) of diastereomer-pure (de>98%) 1-[2(R)-[1(R)-carboxy-2-(3,4,4,-trimethyl-2,5-dioxo-1-imidazolidinyl)ethyl]-3-cyclopentylpropionyl]piperidine (IX), m.p. 111-114°, was obtained. IR (KBr): 1770m and 1715s (C═O).

Provenance & Evidence