Activation of Styrenes toward Diels−Alder Cycloadditions by Osmium(II): Synthesis of Stereodefined Decalin Ring Systems

The complex [Os(NH 3 ) 5 (η 2 -anisole)] 2+ reacts with acetals or Michael acceptors to form 4-methoxystyrene complexes that are exclusively coordinated at the arene (η 2 ). These styrene complexes are active dienes and readily participate in Diels−Alder reactions with electron-deficient olefins to form tetrahydronaphthalene complexes. The cycloadducts are formed typically as single diastereomers and are valuable as precursors to functionalized tetralins and decalins.