for the ortholithiation of 3-aryl and 3-styryl furans has been uncovered wherein lithiation occurs preferentially at the sterically encumbered 2-position. The results are attributed, at least in part, to stabilization of the intermediate furyl anion by through-space donation of pi-electron density from the substituent appended at the 3-position to the lithium cation. This ortholithiation reaction
Cationic Gold(I)-Mediated Intramolecular Cyclization of 3-Alkyne-1,2-diols and 1-Amino-3-alkyn-2-ols: A Practical Route to Furans and Pyrroles
作者:Masahiro Egi、Kenji Azechi、Shuji Akai
DOI:10.1021/ol901942t
日期:2009.11.5
The intramolecular cyclizations of the 3-alkyne-1,2-diols and the 1-amino-3-alkyn-2-ols with a low catalyst loading (0.05-0.5 mol %) of (Ph3P)AuCl-AgNTf2 or (Ph3P)AuCl-AgOTf proceeded at room temperature to provide a variety of substituted furans and pyrroles in excellent yields (85-98% yields). This method is also fully applicable to the conversion of several dozen grams of the substrate using only 0.05 mol % each of the Au and Ag catalysts.