[reaction: see text] The use of 2-(trimethylsilyloxy)furan derivatives as dianion equivalents leads to a general and connective spiroannulation protocol for the efficient preparation of spirocyclic butenolides.
Maulide, N., & Marko, I. (2006). 2-(Trimethylsilyloxy)furan as a dianion equivalent: a two-step synthesis of functionalized spirocyclic butenolides. Organic Letters, 8(17), 3705-3707. https://doi.org/10.1021/ol061284g (Original work published 2006)