Gold(i)-catalysed cyclisation of (E)-ketene-N,O-acetals: a synthetic route toward spiro-oxazole-γ-lactones†‡

In this study, we developed a cascade 5,5-cyclisation of internal ketene-N,O-acetals utilizing homogeneous Au(i) catalysis. This process involves an initial 5-exo-dig carbocyclisation, followed by a 5-exo-dig heterocyclisation that stereoselectively incorporates the O-atom of a water molecule into an N-tethered propargyl alkyne. This sequential reaction results in the formation of one C–C, two C–O, and two C–I bonds, ultimately leading to the synthesis of spiro-α-iodo-γ-lactone structures featuring oxazole rings in good yields.