1-Bromo-1-lithioethene: A Practical Reagent in Organic Synthesis
摘要:
A reliable preparative scale synthesis of 1-bromo-1-lithioethene is reported. This reagent undergoes clean 1,2-addition with a range of aldehydes and ketones at -110 degrees C to afford the corresponding 2-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 various 1-substituted 1-bromoethene products. Unexpectedly high diastereoselectivities were observed during the addition of 1-bromo-1-lithioethene to alpha-siloxy aldehydes (typically 10:1, Felkin-Ahn control) and protected ketopyranose and ketofuranose sugars (>= 10:1, addition from the less-hindered face). The title organolithium reagent possesses relatively low basicity at low temperature, and is compatible with a variety of common protecting groups. We believe that these unusual properties of 1-bronio-1-lithioethene may originate from the specific crystalline structure of the reagent in which lithium is coordinatively saturated and thus unavailable for chelation.
Henry, Bulletin de la Societe Chimique de France, 1884, vol. <2>42, p. 262
作者:Henry
DOI:——
日期:——
1-Bromo-1-lithioethene: A Practical Reagent in Organic Synthesis
作者:Yehor Y. Novikov、Paul Sampson
DOI:10.1021/jo051125v
日期:2005.12.1
A reliable preparative scale synthesis of 1-bromo-1-lithioethene is reported. This reagent undergoes clean 1,2-addition with a range of aldehydes and ketones at -110 degrees C to afford the corresponding 2-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 various 1-substituted 1-bromoethene products. Unexpectedly high diastereoselectivities were observed during the addition of 1-bromo-1-lithioethene to alpha-siloxy aldehydes (typically 10:1, Felkin-Ahn control) and protected ketopyranose and ketofuranose sugars (>= 10:1, addition from the less-hindered face). The title organolithium reagent possesses relatively low basicity at low temperature, and is compatible with a variety of common protecting groups. We believe that these unusual properties of 1-bronio-1-lithioethene may originate from the specific crystalline structure of the reagent in which lithium is coordinatively saturated and thus unavailable for chelation.