1,3‐(C → O) Silyl Shift in α‐Diazo α‐Silyl Ketones: Cycloaddition Reactions and Kinetic Proof for the β‐Siloxydiazoalkene Intermediate

The 1 : 1 cycloadducts 3 and 4 with norbornene and N-phenylmaleimide (NPM), respectively, can be regarded as direct trapping products of the diazoalkenes 2. A kinetic analysis of the trapping reaction with NPM rules out a [3+2] cycloaddition of the diazoketone 1 with formation of 5 and spontaneous silylketone–silyl enol ether isomerization to 4. The conversion of 1 into 2 already takes place at 25–60°C. R  tBu or p-NO2C6H4.