Using a two-step reduction/metalation procedure, highly stable chiral carbenium ions are transformed into reactive carbanion intermediates. Interesting polar ketone and thioamide products are the results of this umpolung that occurs with complete retention of configuration of the helical backbone.

Various 3-iodo-4-methoxypyridin-2-ones and related pyrone and coumarin derivatives have been demonstrated as readily available precursors of 2-substituted furan-fused heterocycles by means of in situ sequential Sonogashira-acetylide coupling, dealkylation, and regioselective furan annulation reactions. A Et3N-induced S(N)2 process has been established that accounts for the dealkylation process.

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N-Methyl-4-alkoxy-3-alkynylpyridin-2(1H)-ones readily undergo iodine-promoted 5-endo-heteroannulation under mild conditions to 3-iodofuropyridinium triiodide salts in moderate to good yields. The latter may be dealkylated in situ upon exposure to an iodide anion to provide the corresponding 3-iodofuro[2,3-b]pyridin-4(1H)-ones. The same strategy applies to the formation of furo[2,3-b]quinolin-4(9H)-ones.

3,5-Dihalogeno-4-methoxy-N-methylpyridin-2(1H)-ones have been shown to undergo single Suzuki coupling reactions in a site-selective fashion. Monoarylations occur at the C-5 position preferentially, thus leaving the remaining C-3 halide free for further functionalization, to finally access differentially 3,5-disubstituted 2-pyridones. This two-step strategy has been applied to the elaboration of the 3-acyl-5-aryl-4-oxy-2-pyridone subunit that is prevalent in numerous bioactive natural products. [reaction: see text].

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The products are relevant for the preparation of various bioactive compounds. -(CONREAUX, D.; BOSSHARTH, E.; MONTEIRO, N.; DESBORDES, P.; VORS, J.-P.; BALME*, G.; Org. Lett. 9 (2007) 2, 271-274; Lab. Synth. Organomet. Mol. Bioact., Univ. Claude Bernard Lyon, F-69622 Villeurbanne, Fr.; Eng.) -R. Steudel 20-128

3-Alkynyl-4-methoxypyridin-2(1H)-ones undergo cyclization via divergent pathways when heated in acetic acid or triethylamine as reagent-solvent under microwave irradiation to furnish selectively furo[2,3-b]pyridin-4-ones or their regioisomeric furo[3,2-c]pyridin-4-ones, respectively. The same strategy applies to the synthesis of furoquinolinones.