Stereoselective Synthesis of 2-(2-Aminoalkyl)- and 1,3-Disubstituted Tetrahydro-1H-pyrido[4,3-b]- Benzofuran and Indole Derivatives.

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