ALLENE-BASED ELECTROPHILE-MEDIATED CYCLIZATIONS - EFFICIENT SYNTHESISOF MEDIUM RING AZACYCLES

While Ag-I- and Pd-II-based electrophiles have limited application in cyclisations of allenic amines leading to 7-membered and larger azacyc les, these rings-may be obtained using iodine as the electrophilic tri gger. Iodination of the N-benzyl derivative 5 gives hexahydroazepine 9 either directly or via the isolable allylic iodide 10. The sulfonamid e-based allylic iodides 11a-e, produced by direct iodination of alleni c sulfonamides 4a-e, cyclise in the presence of NaH, and the product d istribution-12 vs. 13-which depends on the size of rings involved, sho ws a preference towards formation of the larger ring 13. This chemistr y provides a relatively efficient synthesis of 8- 9-, 10- and 11-membe red azacycles 13a-e and C-13 and H-1 NMR correlations have been applie d to assign the (E)/(Z)-alkene geometry of both 13 and related macrocy cles 14.