LEWIS-ACID-INDUCED REACTIONS OF ALPHA-METHOXYGLYCINAMIDE DERIVATIVES WITH SILYL ENOL ETHERS - FORMATION OF 3-AMINO-2-PYRROLIDINONES AND 3-AMINO-2-PYRROLINONES

In order to develop an expedient synthetic route to gamma-oxo-alpha-aminocarboxamides, five different alpha-(alkoxycarbonyl)amino-alpha-methoxyacetamides were subjected to borontrifluoride-etherate-mediated reactions with one silyl ketene acetal and four silyl enol ethers. Reactions of primary and secondary amides did not lead to the desired C-C-bond formation. Reactions of the tertiary N,N-dimethylamide gave the expected gamma-oxo-alpha-aminocarboxamides. The reaction of an N-methoxy-N-trimethylsilylcarboxamide with the ketene acetal also proceeded normally. However, the initial products of the latter amide with silyl enol ethers reacted further by cyclization, respectively, to give a cyclic N-methoxy-N-acyliminium intermediate. Depending on structural features of the enol ether used, this iminium intermediate suffered either proton loss and isomerization to give protected 3-amino-1- methoxy-DELTA-3-pyrrolin-2-ones, or underwent a second coupling with the enol ether to give protected 3-amino-1-methoxypyrrolidin-2-ones.