Synthesis of Furoxans and Isoxazoles via Divergent [2 + 1 + 1 + 1] Annulations of Sulfoxonium Ylides and tBuONO.

We have presented a simple and new method for the divergent assembly of furoxans and isoxazoles in which the [2 + 1 + 1 + 1] annulation reaction of sulfoxonium ylides is reported for the first time. When the reaction was performed using tBuONO as the nitrogen source without metal catalyst, the desired furoxans were obtained in decent yields with wide substrate scope. Isoxazoles bearing three carbonyl groups were achieved when the reaction was conducted using Cu(TFA)2 as catalyst.