Regio- and Stereoselective Preparation of β,γ-Unsaturated Carboxylic Acids by One-Pot Sequential Double 1,6-Addition of Grignard Reagents to Methyl Coumalate

An efficient regio- and stereoselective metal-catalyzed addition of two Grignard reagents (homo-coupling, 2 RMgX or hetero-coupling, R1MgX+R2MgX) to methyl coumalate (methyl 2-oxo-2H-pyran-5-carboxylate) is described. This synthetic approach opens the access to a wide variety of functionalized β,γ-unsaturated carboxylic acids in a modular way. Control of the chemo- and stereoselectivity of this one-pot procedure is discussed.