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.