An efficient asymmetric synthesis of Fmoc- l-cyclopentylglycine via diastereoselective alkylation of glycine enolate equivalent

Abstract

Stereoselective alkylation of the enolate derived from benzyl (2 R,3 S)-(−)-6-oxo-2,3-diphenyl-4-morpholinecarboxylate ( 1 ) with cyclopentyl iodide afforded anti-α-monosubstituted product, benzyl (2 R,3 S,5 S)-(−)-6-oxo-2,3-diphenyl-5-cyclopentyl-4-morpholinecarboxylate ( 3 ) in 60% yield. Catalytic hydrogenolysis over PdCl 2 cleaved the auxiliary ring system to give l-cyclopentylglycine ( 4 ) in 84% yield. Subsequent protection of the α-amino function with Fmoc-OSu gave Fmoc- l-cyclopentylglycine ( 5 ) in high yield.