Transition-Metal-Free BF<sub>3</sub>-Mediated Oxidative and Non-Oxidative Cross-Coupling of Pyridines
作者:Quan Chen、Thierry León、Paul Knochel
DOI:10.1002/anie.201400750
日期:2014.8.11
We report a BF3‐mediated direct alkynylation of pyridines at C(2) by using a variety of alkynyllithium reagents (oxidative cross‐coupling). Moreover, we have developed a novel transition‐metal‐free cross‐coupling method between alkylmagnesium reagents and 4‐substituted pyridines, such as isonicotinonitrile and 4‐chloropyridine, by employing BF3⋅OEt2 as a promoter. The combination of these methods enabled
reagents undergo an addition reaction at position C-2 of pyridines that are rearomatized by oxidative treatment with chloranil. These substituted pyridines can be easily converted into more valuable intermediates. Examples of applications are given as well. Finally, the synthesis of piperidines and lactams via first an oxidativeBF3-mediated addition reaction followed by a NaBH4 reduction or acidic