Scheme 3.

(a) H₄N₂ H₂O (2 equiv.), AcOH (5 equiv.), MeOH, 25 °C, 45 min; (b) pyridine/DIPEA (9:1), 150 °C, 48 h; (c) Pb(OAc)₄ (1.1 equiv.), CH₂CI₂, 0 °C, 30 min (43% of 9 from 2); (c') Pb(OAc)₄ (1.2 equiv.), PhCH₂COOH (50 equiv.) (premixed), CH₂CI₂, 0 °C, 30 min. (36% of 10 from 2); (d) hv (300 nm), EtOAc/benzene (1:1) or MeOH, 25 °C (67–92% for 3, 90% for 4)