Add time:07/24/2019         Source:sciencedirect.com

A convenient methodology which can be tailored to incorporate a chalcogen atom at the C-6 or C-3 position of 2-Methoxypyridine (cas 1628-89-3) (1) was developed. This was achieved by the regioselective lithiation of 1 in the presence and absence of BF3⋅Et2O. The reactions of the 2-methoxypyridine-BF3 adduct with lithium diisopropylamide (LDA) and subsequent trapping with chalcogen and iodomethane furnished a C-6 substituted product. However, the use of uncomplexed 1 led to the lithiation and chalcogenation at the C-3 position. The origin of selectivity in these reactions was studied by quantum chemical analysis. It was found that the coordination between the lithium (on C-6) and the fluoride of BF3 preponderates over the directed metalation ability of the methoxy unit in directing the lithiation process.

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