Selective 1,5-alkylidenecarbene insertion reactions on [3.2.1] oxabicyclic ethers: a new approach toward the AB ring system of ingenol.

Two methods to achieve the formal aldol reaction between acetone and two oxabicyclic [3.2.1] ketones are reported. The trimethylsilyl-protected beta-hydroxy ketones are converted by a Wittig reaction into vinyl chlorides as synthetic precursors to alkylidenecarbenes. Selective 1,5 C-H over 1,5 O-Si insertion has been applied to the synthesis of a model for the ABC ring system of ingenol. Copyright 2004 American Chemical Society