Regioselective Dearomatization of N-Alkylquinolinium and Pyridinium Salts under Morita-Baylis-Hillman Conditions

Morita-Baylis-Hillman reaction employing N-alkylquinolinium salts as electrophiles has been developed. The reaction is promoted by DBU, which acts both as a catalyst activating the electron-poor olefin as well as a base. The dearomatization occurs regioselectively at the C-2 position, delivering a broad range of alpha-(1,2-dihydroquinolin-2-yl)vinyl esters, ketones, and sulfones. The scope of the transformation has also been extended to N-alkylpyridinium salts. For this class of substrates a presence of at least moderately electron-withdrawing substituent in the ring is necessary to attain good reactivity. In particular, N-alkylpyridinium salts containing an ester group undergo the dearomatization regioselectively at the C-4 position, while nitrile and nitro moieties cause the non-selective formation of products of the C-2 and C-6 additions.