Furopyridines. XIII. Reaction of 2‐methylfuro[2,3‐b]‐, ‐[3,2‐b]‐, ‐[2,3‐c]‐ and ‐[3,2‐c]pyridines with lithium diisopropylamide

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AbstractLithiation of 2‐methylfuro[2,3‐b]‐ 1a, ‐[2,3‐c]‐ 1c and ‐[3,2‐c]pyridine 1d with lithium diisopropylamide at −75° and subsequent treatment with deuterium chloride in deuterium oxide afforded 2‐monodeuteriomethyl compounds 2a, 2c and 2d, while 2‐methylfuro[3,2‐b]pyridine 1b gave a mixture of 1b, 2b, 2‐methyl‐3‐deuteriofuro[3,2‐b]pyridine 2′b and 2‐(1‐proynyl)pyridin‐3‐ol 5. The same reaction of 1a at −40° gave 3‐(1,2‐propadienyl)pyridin‐2‐ol 3 and 3‐(2‐propynyl)pyridin‐2‐ol 4. Reaction of the lithio intermediates from 1a, 1c and 1d with benzaldehyde, propionaldehyde and acetone afforded the corresponding alcohol derivatives 6a, 6c, 6d, 7a, 7c, 7d, 8a, 8c and 8d in excellent yield; while the reaction of lithio intermediate from 1b gave the expected alcohols 6b and 8b in lower yields accompanied by formation of 3‐alkylated compounds 9, 11, 12 and compound 5. While reaction of the intermediates from 1a, 1b and 1d with N,N‐dimethylacetamide yielded the 2‐acetonyl compounds 13a, 13b and 13d in good yield, the same reaction of 1c did not give any acetylated product but recovery of the starting compound almost quantitatively.