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

Bromination of [20]smaragdyrin <b>4</b> with N-bromosuccinimide (NBS) gave monobromo[20]smaragdyrin <b>9</b> in 68% under mild conditions but afforded decabromo[20]smaragdyrin <b>8</b> in 64% yield with 20 equiv of NBS at room temperature for 7 days. At 60-65 °C, rearranged nonabrominated product <b>12</b> was obtained along with <b>8</b>. Decabromide <b>8</b> was converted to decabromo[22]smaragdyarrin <b>7</b>, decabromo[22]smaragdyrin BF₂ complex <b>5</b>, and decabromo[20]smaragdyrin BF₂ complex <b>6</b>. 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 <b>13</b> and <b>14</b> were obtained by Suzuki-Miyaura coupling of <b>5</b> with phenyl boronic acid.