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Summary. Both 2,5-trans and 2,5-cis disubstituted 2-tert-butyl-5-(indol-3-yl)methylimidazolidin-4-ones were synthesised and their enolates were prepared using LDA. While the enolate of the 2,5-trans disubstituted derivative could not be methylated, the enolate of the cis-2,5-disubstituted derivative was successfully methylated with methyl iodide to a product which on hydrolysis gave enantiomerically pure -methyl-L-tryptophan.