Vinylogous formamides-5-formyluracils and 4-formylpyrazoles-undergo smooth olefination in THF in the presence of indium metal (0.8 equiv) and BF3.OEt2 (1 equiv) and allyl bromide (1 equiv) to provide the respective diene-substituted heterocycles in a single step. (C) 2004 Elsevier Ltd. All rights reserved.