Synthesis of C-6 and C-3 substituted chalcogen derivatives of 2-methoxypyridine through lithiation of 2-methoxypyridine: An experimental and quantum chemical study
摘要:
A convenient methodology which can be tailored to incorporate a chalcogen atom at the C-6 or C-3 position of 2-methoxypyridine (1) was developed. This was achieved by the regioselective lithiation of 1 in the presence and absence of BF3 center dot 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. (C) 2015 Elsevier B.V. All rights reserved.