The totalsynthesis of the piperidine alkaloid isoprosopinine A (1) and an improved synthesis of isoprosopinine B (2) are reported. The key steps were alkylation of the anions of the sulphones (5) and (6) respectively with the common intermediate bromide (4) and the novel reductive cleavage of the sulphonamides (7) and (8) with sodium-amalgam.