| Abstract
| - A reliable preparative scale synthesis of 1-bromo-1-lithioethene is reported. This reagent undergoesclean 1,2-addition with a range of aldehydes and ketones at −110 °C to afford the corresponding2-bromo-1-alken-3-ols in moderate to excellent yield. Trapping with other electrophiles (acylsilanes,chlorosilanes, tributyltin chloride, iodine) cleanly provides practically useful yields of various1-substituted 1-bromoethene products. Unexpectedly high diastereoselectivities were observedduring the addition of 1-bromo-1-lithioethene to α-siloxy aldehydes (typically 10:1, Felkin−Ahncontrol) and protected ketopyranose and ketofuranose sugars (≥10:1, addition from the less-hinderedface). The title organolithium reagent possesses relatively low basicity at low temperature, and iscompatible with a variety of common protecting groups. We believe that these unusual propertiesof 1-bromo-1-lithioethene may originate from the specific crystalline structure of the reagent inwhich lithium is coordinatively saturated and thus unavailable for chelation.
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