Synthesis of 2,6-Disubstituted Pyridines, Polypyridinyls, and Annulated Pyridines

Article abstract of DOI:10.1021/jo00137a001

1,5-Enediones containing a variety of substituents in the 1,5-positions are formed in good yields by the reaction of methyl ketone enolates, generated with potassium tert-butoxide, with α-oxoketene dithioacetals, the latter being prepared from alkyl, cycloalkyl, aryl, or heteryl methyl ketones, NaH, CS2, and CH3I.Ring closure of the 1,5-enediones with NH4OAc gave 2,6-disubstituted 4-(methylthio)pyridines in good to excellent yields.This procedure is particularly suited for the synthesis of 2,6-diheterylpyridines and provides a simple synthesis of terpyridinyl and other oligopyridines.The methylthio groups in the α-oxoketene dithioacetals may be oxidized to the mono- and disulfoxides with m-chloroperbenzoic acid, but with excess peracid, in addition to oxidation to the disulfone, epoxidation of the double bond also occurs.The pyridine 4-methylthio substituent may also be oxidized to the sulfoxide and to the sulfone, and the latter may be displaced with cyanide ion to form the corresponding 4-carbonitrile.