Spirolactonization Reformatsky reaction

Similar condensations can be accomplished with other types of stabilized carbanions, e.g. sulfonyl anions, as illustrated by equation (81). The resulting sulfonyl lactone (228) eliminates sulfinic acid on treatment with p-TsOH to furnish the a,3-unsaturated system (229).Spirolactonization is the result of the Reformatsky reaction of ester (231) with cyclic ketones. In equation (82), this reaction is applied to the synthesis of the lysergic acid precursor (232), which is formed stereoselectively from (230). ... 

Figueredo and coworkers were driven by the total synthesis of a polycyclic natural molecule (the putative structure of stemonidine) [22] when they reported their Reformatsky-type reaction for the diastereoselective construction of spiro-a-methylene-y-butyrolactone 48. Reaction of the starting ketone 47 with ethyl bromomethylacrylate and zinc led to the formation of the desired spirolactone 48 in 86% yield and with complete facial selectivity (Scheme 9.13). 

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