Synthesis of (R)-Boc-2-methylproline via a Memory of Chirality Cyclization. Application to the Synthesis of Veliparib, a Poly(ADP-ribose) Polymerase Inhibitor

(R)-Boc-2-methylproline (3a) was synthesized in good yield with excellent stereochemical control from alanine benzyl ester hydrochloride 11. The process, which is based on a modification of one described by Kawabata, proceeds in four steps and requires no chromatography. The product (R)-Boc-2-methylproline (3a) was then carried forward in three steps to produce veliparib 1, a poly(ADP-ribose) polymerase inhibitor.