Selective Bromination and Perbromination of 5,10,19-Trimesityl[20]smaragdyrin

Bromination of [20]smaragdyrin 4 with N-bromosuccinimide (NBS) gave monobromo[20]smaragdyrin 9 in 68% under mild conditions but afforded decabromo[20]smaragdyrin 8 in 64% yield with 20 equiv of NBS at room temperature for 7 days. At 60-65 °C, rearranged nonabrominated product 12 was obtained along with 8. Decabromide 8 was converted to decabromo[22]smaragdyarrin 7, decabromo[22]smaragdyrin BF₂ complex 5, and decabromo[20]smaragdyrin BF₂ complex 6. These decabrominated smagdyrin derivatives show distorted nonplanar structures with diatropic and paratropic ring currents depending upon the number of conjugated π-electrons. Decaphenyl[22]- and [24]-smaragdyrin BF₂ complexes 13 and 14 were obtained by Suzuki-Miyaura coupling of 5 with phenyl boronic acid.