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.