C4‐Regioselective Dearomatization of Quinolinium Salts via Morita‐Baylis‐Hillman Reaction

An intermolecular Morita‐Baylis‐Hillman reaction employing N‐benzylquinolinium salts as electrophiles was developed. The reaction proceeds through a C4‐selective dearomatization of the quinolinium substrate, contrary to the C2‐regioselectivity that was observed in our previous report on a similar process. The switch in the regioselectivity was accomplished through the change of the counterion in the quinolinium salt to PF6– and the alteration of the reaction conditions, such as the application of a different catalyst (DABCO). The reaction allows for the preparation of functional group‐rich products featuring the important 1,4‐dihydroquinoline scaffold, complementing the earlier method which provides the corresponding 1,2‐dihydroquinoline counterparts. The developed reaction is compatible with a range of substrates that also encompasses acridinium salts.