Copper-mediated 3-N-arylation of flavins

A generally applicable method for the direct 3-N-arylation of flavins using arylboronic acids and copper acetate was developed. The reaction conditions were optimized considering the lability of flavins in basic conditions and thermal heating. Donor-and acceptor-substituted arylboronic acids were used yielding 3-N-arylflavins in moderate to good yields by C(aryl)-N(imide) bond formation. UV and fluorescence measurements indicate an orthogonal orientation of the additional aromatic substituent to the flavin ring system. The arene substituent is not electronically coupled to the flavin pi-system in the ground state, but electron-rich arene substituents in 3-N position significantly reduce the flavin emission intensity.