[en] Methodology applicable to the synthesis of no-carrier-added [O-methyl-¹¹C]alfentanil was developed. The sequence consisted of [¹¹C]methylation and propionylation of N-aryl-4-(hydroxymethyl)-4-(N-anilino)-piperidines 1a and 1c, followed by the chemoselective hydrolysis of bulk byproducts to facilitate isolation of the NCA carbon-11-labeled product by prep-HPLC. All three steps could be performed without isolation of intermediates in a single reaction vessel. (author)