Indium-Mediated Asymmetric Intramolecular Allenylation of N-tert-Butanesulfinyl Imines: Efficient and Practical Access to Chiral 3-Allenyl-4-aminochromanes

An efficient method for the preparation of highly optically active 3-allenyl- and 3-vinyl-4-aminochromanes by In-mediated intramolecular cyclization has been developed. The synthetic utilities of the approach were demonstrated by the construction of various chiral polycyclic heterocycles, especially the interesting spiroheterocyclic compound 9 and steroid analogue 10.