New method for activation of aldimines in cycloaddition of lithium ynolates with N-2-methoxyphenyl imines leading to β-lactams

The cycloaddition of the N-2-methoxyphenyl aldimines with lithium ynolates was efficiently accelerated via chelation to give β-lactam enolates, which immediately reacted with one more equivalent of the imine to give β-lactams (2:1 adducts) in good yields, while N-4-methoxyphenyl imines were inert towards lithium ynolates.