Synthesis of γ,δ-Unsaturated α-Methyl-α-amino Acids via Coupling of Allylsilanes with an α-Methylglycine Cation Equivalent

Intermolecular reactions of an alpha-methylglycine cation equivalent [methyl N-formyl-2-trimethylsiloxyalanine (6)] with allylsilanes, induced by trimethylsilyl trifluoromethanesulfonate, lead to protected gamma,delta-unsaturated alpha-methyl-alpha-amino acids. A side reaction is the formation of a 2,3-dehydroalanine derivative 13, by proton loss from the cationic intermediate. The coupling products can be efficiently deprotected to the free alpha-amino acids.