Although thioamides generally undergo a reductive alkylation process when they are treated with a Grignard reagent in the presence of Ti(OiPr)4, substrates fitted with a but-3-enyl substitution at the nitrogen atom are shown to be converted into bicyclic aminocyclopropanes. These reactions are compared with the similar cyclisations of the corresponding carboxylic amide substrates. A mechanistic study is provided. Coincidently, new reagent systems are identified for the mediation of the same transformation.