Steric hindrance-controlled Pd(0)-catalyzed coupling-cyclization of 2,3-allenamides and organic iodides. An efficient synthesis of iminolactones and gamma-hydroxy-gamma-lactams.

Under the catalysis of 1 mol % Pd(PPh3)4, the reaction of 4,4-disubstituted 2,3-allenamides and organic iodides in toluene afforded iminolactones stereospecifically in >90% yields using K2CO3 (2 equiv)-5 mol % TBAB as the base. A similar reaction with 4-monosubstituted 2,3-allenamides afforded gamma-hydroxy-gamma-lactams in relatively lower yields. The N/O-attack selectivity may be determined by the steric effect at the 4-position of 2,3-allenamides.