Chemo- and Diastereoselective Entries into All-Carbon α-Quaternary Aldehydes via C-C Insertion of 4-Diazoisoquinolin-3-ones into C-CHO Bonds.

Herein, we describe a chemo- and diastereoselective formal C-C insertion reaction of 1,2-disubstituted 4-diazo-3(2 H )-isoquinolones and 4-diazoisochroman-3-one into C-CHO bonds of aldehydes, delivering all-carbon α-quaternary aldehydes bearing medicinally important 1,4-dihydro-3(2 H )-isoquinolone scaffold. Our protocol is enabled by the preferential 1,2-carbon migration over more common 1,2- H shift. The corresponding reaction tolerates a wide range of functionalities in both aldehyde and diazo components, giving the target homologated aldehydes in generally high yields. The synthetic utility of this method has been further showcased by some transformations of the formyl moiety.