Titanium isopropoxide-mediated -selective synthesis of 3,4-substituted butyrolactones from CO.

We report a Ti(OiPr)-mediated multicomponent reaction, which produces 3,4-substituted -δ-lactones from alkyl magnesium chloride, benzaldehyde and CO. The key intermediate, titanacyclopropane, is formed from Ti(OiPr) and a Grignard reagent, which enables 1,2-dinucleophilic reactivity that is used to insert carbon dioxide and an aldehyde. An alternative reaction route is also described where a primary alkene is used to create the titanacyclopropane.