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New J. Chem., 2007, 31, 486 - 495, DOI: 10.1039/b701628j

On the origins of diastereoselectivity in the alkylation of diketopiperazine enolates

Steven D. Bull, Stephen G. Davies, A. Christopher Garner, Alastair L. Parkes, Paul M. Roberts, Thomas G. R. Sellers, Andrew D. Smith, Juan A. Tamayo, James E. Thomson and Richard J. Vickers

High levels of diastereoselectivity are observed for benzylation of the lithium enolates of (S)-N,N-bis-para-methoxybenzyl-3-iso-propyl-piperazine-2,5-dione, (S)-N(1)-para-methoxybenzyl-N(4)-methyl-3-iso-propyl-piperazine-2,5-dione and (S)-N(1)-methyl-N(4)-para-methoxybenzyl-3-iso-propyl-piperazine-2,5-dione. These data suggest that the high diastereofacial selectivity observed for alkylation of these diketopiperazine templates is mainly a consequence of the relay of stereochemical information from C(3) to C(6) via the influence of 1,2-torsional strain introduced by the N-alkyl substituents, rather than through minimisation of steric interactions alone.

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