Diastereoselective cascade reactions toward substituted diazaindeno[2,1-α]phenanthrenes

A cascade sequence between cyclic hemiacetals and tryptamines was developed, which provided efficient access to highly substituted diazaindeno[2,1-α]phenanthrenes in moderate to good yields with high diastereoselectivities and good to excellent enantioselectivities. Hemiacetals were prepared by asymmetric organocatalyzed conjugate addition of cyclic 1,3-diketones to α,β-unsaturated aldehydes. Hemiacetals with various R1, both aromatic and aliphatic, were examined for the cascade sequence.