Double fragmentation in cation radicals. An example in the NADH analogues series

The cation radical of 9-tert-butyl-N-methylacridan, generated electrochemic ally or photochemically, offers, in the presence of strong bases, a remarka ble example of a double fragmentation. Whereas in acidic or weakly basic me dia the tert-butyl radical is cleaved with concomitant formation of the met hylacridinium cation, the presence of a strong base triggers the cleavage o f both the methyl group borne by the nitrogen atom and the tert-butyl group on C-9 leading to acridine, formaldehyde and the tert-butyl anion, even th ough methylacridinium cation is stable under these conditions. The origin o f this unprecedented behavior resides in the prior deprotonation of the met hyl group borne by the nitrogen atom which outruns the usual deprotonation at the 9-carbon because this is slowed by the steric hindrance due to the p resence of the tert-butyl group. (C) 1998 John Wiley & Sons, Ltd.