Unexpected B-ring regioselective di-nitration of diosmetin, a Citrus flavonoid

Nitration in position C-8 of diosmetin, an easily available citroflavonoid, was studied in order to gain access to original analogs. The one-step nitration proved impossible, as mono or di-nitration on C-2′ and C-6′ positions on the lateral B ring of the molecule was exclusively observed. This surprisingly straightforward di-nitration of ring B, showing a lack of reactivity of ring A despite its high activation, has never been mentioned to date. Nitration in position C-8 was therefore performed in five steps, requiring selective deactivation of ring B.

Nitration of diosmetin occurred only on the B-ring at C-2′ and C-6′, but not on the however highly activated ring A. Nitration in position C-8 was therefore performed in five steps, requiring selective deactivation of ring B.