Regioselective synthesis of (±)-gabaculine hydrochloride

3- Cyclohexenecarboxylic acid (2) has been functionalized to the protected amino acid 5 in a novel reaction sequence, the crucial step being the acid catalysed cyclization of the γ, δ-unsaturated isocyanate 3 to the bicyclic lactam 4. 5 was converted into gabaculine hydrochloride (1 · HCl).