Single-electron/pericyclic cascade for the synthesis of dienes.

The highly efficient and diastereoselective synthesis of E dienes has been accomplished through radical cyclization of bromoallyl hydrazones. This methodology has been further extended to generate these products through a one-pot condensation/radical cyclization/cycloreversion cascade from simple aldehyde starting materials in high yields (>75%) and high diastereoselectivities (>95:5). Mechanistic investigations suggest that the cascade reaction proceeds through a cyclic diazene intermediate prior to the cycloreversion.