alpha-Ethoxyvinyllithium: An Unexpected Polymeric Structure—Tetrameric Subunits Linked by Li-C pi Interactions

摘要

Serving as an acyl anion equivalent, a-ethoxyvinyllithium (1) is a widely used synthetic reagent. We now report the complex X-ray structure of unsolvated 1. as well as NMR spectroscopic evidence for its nature in THF. In general, oreanolithium systemswith a-halogen or alpha-oxygen substituents (R~1R~2CXLi) have "carbenoid" character, with bridging lithium and elongated C-X bonds. Crystals of 1 (synthesized by tin/lithium exchange) were obtained from hexane in the absence of cosolvems. The structureof 1 adopts a self-assembled, polymeric chain in the solid state (Fig. l). The asymmetric unit contains six H,C = C(Li)OEt molecules. Four of them are aggregated to form a distorted cubic Li_4C_4 tetramer, the remaining two generate a second te-tramer bya C_2 axis (Fig. la).