Methyl 2-(Benzyloxycarbonylamino)-2-cyclopropylideneacetate: A Versatile Building Block for Cyclopropyl-Containing Amino Acids

Abstract

Methyl 2-(benzyloxycarbonylamino)-2-cyclopropylideneacetate (2) was prepared in nine steps starting from L-serine in an overall yield of 24 %. It has been demonstrated to be reasonably reactive in Michael additions of various nucleophiles (6 examples, 75-98%) yields) as well as Diels-Alder reactions, both leading to new cyclopropyl-containing amino acids in protected form. An application of 2 in the synthesis of methyl 4-tert-butoxycarbonylmethyl-5-oxo-4,7-diazaspiro-[2.5]octane-8-carboxylate (15), a precursor for geometrically constrained bicyclic peptidomimetics of type 16, has also been proved. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)