Yb(OTf)3-Catalyzed Formal (4 + 3) Cycloaddition Reactions of 3-Benzylideneindoline-2-thiones with Donor-Acceptor Cyclopropanes.

A Yb-(OTf)(3)-catalyzed formal (4 + 3) cycloaddition reaction of donor-acceptor cyclopropanes with 3-benzylideneindoline-2-thiones as sulfur-containing 4 pi components has been successfully achieved. A series of functionalized 5,10-dihydro-2H-thiepino-[2,3-b]-indole derivatives were synthesized with good yields and moderate to good diastereoselectivity. The reaction described herein represented the inaugural (4 + 3) cycloaddition of 3-benzylideneindoline-2-thiones.