Four-Step Synthesis of the β-Pyridylethylamine Core via Ring Opening of Pyrrolidines

-methylazomethine ylide gives rise to a wide range of pyrrolidines via [3 + 2] cycloaddition reaction with enones or one-step domino pyrrolidination of active methylene compounds. Treatment with alkyl halide and ring cleavage of the resulting quaternary ammonium salt of pyrrolidines in the presence of active methylene compounds provide α-(β-dialkylaminoethyl)-1,5-diketones or 1,5-ketoesters in good to high overall yields over three steps. Subsequent cyclization with ammonium acetate in TFEA or HFIP affords 3-pyridylethylamines and 5-pyridonylethylamines in 22-76% overall yields.