Synthesis of furans by base-catalyzed cyclization-isomerization of .beta.- and .gamma.-alkynyl allylic alcohols
摘要:
Beta- and gamma-alkylyl allylic alcohols 3, 13, 26, available through Pd-mediated coupling of appropriate vinylic halides and terminal alkynes, cyclize and subsequently isomerize to furans 4, 17, and 32 upon treatment with KO-t-Bu in t-BuOH-THF at 25-60-degrees-C. The methodology has been used to prepare 2,3-, 2,4-, and 2,3,5-substituted furans. Reactions in t-BuOD as cosolvent lead to deuterium incorporation consistent with concurrent pathways in which direct 5-exo-dig or 5-endo-dig cyclization of the alkynyl allylic alcohol competes with prior isomerization to an allene intermediate which subsequently cyclizes by 5-exo- or 5-endo-dig pathways.
Lespieau, Annales de Chimie (Cachan, France), 1912, vol. <8>27, p. 169
作者:Lespieau
DOI:——
日期:——
1-Bromo-1-lithioethene: A Practical Reagent for the Efficient Preparation of 2-Bromo-1-alken-3-ols
作者:Yehor Y. Novikov、Paul Sampson
DOI:10.1021/ol034594x
日期:2003.6.1
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 -105 degreesC to afford the corresponding 2-bromo-1-alken-3-ols in moderate to excellent yield. Efficient diastereoselective addition to alpha-siloxy and alpha-methylcyclohexanones, as well as protected 3-keto furanose sugars, is achieved in the presence of 10 mol % CeBr3. The resulting bromoallylic alcohol adducts have considerable potential as synthetic building blocks.
Lespieau, Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, 1911, vol. 152, p. 879