Stereoselective Synthesis of 2‑(2-Aminoalkyl)- and 1,3-Disubstituted Tetrahydro‑1<i>H</i>‑pyrido[4,3‑<i>b</i>]- Benzofuran and Indole Derivatives

The addition of an allenyl indium intermediate to chiral <i>N</i>-<i>tert</i>-butanesulfinyl imines <b>7</b> proceeds with high levels of diastereocontrol. The resulting homopropargylic amine derivatives <b>10</b> were transformed into 2-(2-aminoalkyl)­benzofuran and indole derivatives <b>13</b> and <b>19</b>, after Sonogashira coupling with <i>o</i>-iodophenol or <i>o</i>-iodoaniline, followed by formation of the heteroaromatic ring through an intramolecular cyclization. Enantioenriched tetrahydropyrido-benzofuran and indole derivatives <b>16</b> and <b>21</b> were prepared through a Pictet-Spengler condensation of the free amines derived from compounds <b>15</b> and <b>20</b>, involving the nucleophilic 3-position of the benzofuran or indole moiety