What is a key feature of the SN2 reaction mechanism in N-phthalimidomalonic ester synthesis?

The nucleophile attacks from the same side as the leaving group.

The nucleophile attacks the electrophile in a single concerted step, leading to inversion of configuration.

The nucleophile attacks the electrophile in two separate steps, resulting in racemization.

The nucleophile forms a temporary carbocation intermediate.