Nickel-Catalyzed Formal [3+2+2] Cycloadditions of Bis(trimethylsilyl)cyclopropanone With Diynes: A Concise Approach to Functionalized Hydroazulene Derivatives.

Hydroazulene derivatives are significant structural motifs found in natural products and functional organic molecules, and it is important to develop efficient methods for their preparation. In this study, we report the development of formal [3+2+2] cycloaddition chemistry involving 1,6-diynes and cis-2,3-bis(trimethylsilyl)cyclopropanone as a new synthetic approach to functionalized hydroazulene derivatives. The hydroazulene framework is efficiently constructed using the developed reaction, with synthetically versatile functional groups introduced in a single operation. An unusual rearrangement process consistent with a formal [1,7]-silyl migration from the C7 to C6 position of the hydroazulene framework was observed during the course of the transformation. The synthetic utility of the proposed method is demonstrated by further transforming the resulting silylated hydroazulene derivatives into a variety of versatile building blocks. This study provides a new strategy for constructing and functionalizing hydroazulene skeletons as well as new insight into the reactivities of cyclopropanone-derived intermediates.