Yield:-

Reaction Conditions:

with trifluoroacetic acid in dichloromethane

Steps:

3.A 3A.
3A. Preparation of (4) where R ² is Hydrogen, and R ³ and R ⁴ when taken together with the Carbon to which they are attached represent N-CBZ-piperidine. a Compound of Formula (4a) Trifluoroacetic acid (10 ml) was added to 4-tert-butoxycarbonylmethylene-N-CBZ-piperidine (20 g, 60.3 mmol) in methylene chloride (30 ml) and the solution was stirred at room temperature for 1.5 hours. After evaporation of the solvent, the residue was triturated with diethyl ether to give 4-carboxymethylene-N-CBZ-piperidine as a crystalline white solid.

References:

F. HOFFMANN-LA ROCHE AG;AGOURON PHARMACEUTICALS, INC. EP780386, 1997, A1