Iron(II)-catalyzed Oxidative Coupling of Vicinal Diols and 2-Amino-1,4-naphthoquinone for the Synthesis of Pyrrolonaphthoquinones and Furanonaphthoquinones

Direct oxidative coupling of vicinal diols with 2-aminonaphthoquinones has been studied for the selective synthesis of benzo[f]indole-4,9-diones at a moderate temperature. In the presence of an environmentally benign iron catalyst, the vicinal diols were oxidized to alpha-hydroxy carbonyl compounds. Subsequently, 2-amino naphthoquinone reacted with the resultant alpha-hydroxy carbonyl compound through tandem N-C and C-C bond formation to afford a vast range of pyrrolonaphthoquinones in remarkable yield. Interestingly, when the 1,2-propanediol was used, the secondary alcohol group was oxidized preferably by resulting in the 2-methyl pyrrolonaphthoquinones as the major regioisomer. The synthetic utility of the current strategy was extended for one-step delivery of natural products, such as 3-methyl-1H-benzo[f]indole-4,9-dione (a secondary metabolite isolated from Goniothalamus tapis Miq. with anti-PAF activity), antibiotic utahmycin B (3-methyl-1H-benzo[f]indole-4,9-dione), cytotoxic avicequinone B and anti-viral FNQ3 (2-methyl-naphtho[2,3-b]furan-4,9-dione).

Automated summary

The study focused on the direct oxidative coupling of vicinal diols with 2-aminonaphthoquinones for the selective synthesis of benzo[f]indole-4,9-diones at a moderate temperature. The environmentally benign iron catalyst was found to effectively oxidize the vicinal diols to alpha-hydroxy carbonyl compounds, resulting in a vast range of pyrrolonaphthoquinones in remarkable yield. Interestingly, the use of 1,2-propanediol led to the selective oxidation of the secondary alcohol group, producing 2-methyl pyrrolonaphthoquinones as the major regioisomer.