Studies on the reduction and reductive alkylation of amino acid-derived spirocyclic 2,6-dioxopiperazines

The regio- and diastereoselective reduction and reductive alkylation of 3-spiro-2,6-dioxopiperazines are described via a two-step process, which involves addition of NaBH 4 or Grignard reagents, followed by TFA-mediated dehydration with a second NaBH 4 addition. The results show that the reactivity...

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Bibliographic Details
Published in:Tetrahedron 2007-03, Vol.63 (12), p.2675-2683
Main Authors: González-Vera, Juan A., Ventosa-Andrés, Pilar, Casey, Joanne, García-López, M. Teresa, Herranz, Rosario
Format: Article
Language:English
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Summary:The regio- and diastereoselective reduction and reductive alkylation of 3-spiro-2,6-dioxopiperazines are described via a two-step process, which involves addition of NaBH 4 or Grignard reagents, followed by TFA-mediated dehydration with a second NaBH 4 addition. The results show that the reactivity of 2,6-dioxopiperazines is limited by their steric hindrance and by the volume of the nucleophile, which preferably add to the C 6 carbonylic carbon with complete diastereoselectivity. The diastereoselectivity of the first step is mainly governed by electronic factors, which direct the addition of the nucleophile from the most hindered face, while in the second step, the NaBH 4 attacks from the less crowded face. This second step proceeds with partial or complete racemization. [Display omitted]
ISSN:0040-4020
1464-5416
DOI:10.1016/j.tet.2007.01.022