Furopyridines. II. Bromination and nitration of furo[2,3‐<i>b</i>]‐, furo[3,2‐<i>b</i>]‐, furo[2,3‐<i>c</i>]‐ and furo[3,2‐<i>c</i>]pyridine

<jats:title>Abstract</jats:title><jats:p>In order to reveal the reactivities of furopyridines, we undertook bromination and nitration of four furopyridines (<jats:bold>1, 2, 3</jats:bold> and <jats:bold>4</jats:bold>) whose chemical properties had been almost unknown. Bromination of <jats:bold>1, 2, 3</jats:bold> and <jats:bold>4</jats:bold> gave the corresponding <jats:italic>trans</jats:italic>‐2,3‐dibromo‐2,3‐dihydro derivatives <jats:bold>6, 8, 10</jats:bold> and <jats:bold>12</jats:bold>, respectively, which were converted to 3‐bromofuropyridines <jats:bold>7, 9, 11</jats:bold> and <jats:bold>13</jats:bold> by treatment with sodium hydroxide in aqueous methanol. Nitration of <jats:bold>1</jats:bold> with a mixture of fuming nitric acid and sulfuric acid afforded a mixture of addition products <jats:bold>14a, 14b</jats:bold> and <jats:bold>14c</jats:bold> and 2‐nitro derivative <jats:bold>15</jats:bold>. Both <jats:bold>14a</jats:bold> and <jats:bold>14b</jats:bold> were easily converted to <jats:bold>15</jats:bold> by treatment with sodium bicarbonate. Compound <jats:bold>2</jats:bold> was nitrated to give a mixture of <jats:italic>cis</jats:italic>‐ and <jats:italic>trans</jats:italic>‐2‐nitro‐3‐hydroxy‐2,3‐dihydro derivative <jats:bold>16a</jats:bold> and <jats:bold>16b</jats:bold> and 2‐nitro derivative <jats:bold>17</jats:bold>. The <jats:italic>cis</jats:italic> isomer <jats:bold>16a</jats:bold> was transformed to the <jats:italic>trans</jats:italic> isomer <jats:bold>16b</jats:bold> by refluxing on silica gel in ethyl acetate. Compound <jats:bold>16b</jats:bold> was dehydrated with acetic anhydride to give <jats:bold>17</jats:bold>. Nitration of <jats:bold>3</jats:bold> gave a nitrolic acid derivative <jats:bold>20</jats:bold>. Nitration of <jats:bold>4</jats:bold> gave a mixture of 2‐nitro derivative <jats:bold>22</jats:bold> and 3‐(trinitromethyl)pyridin‐4‐ol (<jats:bold>23</jats:bold>). The structures of <jats:bold>20</jats:bold> and <jats:bold>23</jats:bold> were established by single crystal X‐ray analysis. The differences of behavior observed in these reactions are discussed in connection with the results of the determination of p<jats:italic>K</jats:italic>a values and the relative reactivities of deuteriodeprotonation of these furopyridines.</jats:p>