7-Chloroquinoline: a versatile intermediate for the synthesis of 7-substituted quinolines

A practical synthesis of 7-mono-substituted quinolines has been achieved. Selective reduction of the inexpensive commercial reagent 4,7-dichloroquinoline affords 7-chloroquinoline, which has been converted into more complex 7-mono-substituted quinolines through a series of Pd-catalyzed cross coupling reactions. These studies include the first examples of Suzuki reactions for the preparation of 7-mono-substituted quinolines as well as the first application of the Sonagashira reaction for the synthesis of 7-substituted quinolines. This strategy has been extended to the preparation of 2,7-di-substituted quinolines.