An efficient metal-free protocol has been developed for the sp(3) C-H bond oxidation of 2-methylquinolines in the presence of PIDA under microwave irradiation, providing 2-quinolinecarboxaldehydes with moderate to high yields and excellent selectivities. A wide range of 2-quinolinecarboxaldehydes with different functional groups have been synthesized. A tentative mechanism has been presented to explain this highly selective oxidation process. (C) 2016 Elsevier Ltd. All rights reserved.