Highly Stereoselective Intramolecular Michael Addition Using α-Sulfinyl Vinyllithium as an Unprecedented Michael Donor

The first example of an asymmetric intramolecular Michael addition reaction using α-lithiated vinylic sulfoxide as a Michael donor is reported. Michael addition of the α-lithiated vinylic sulfoxide to (<i>Z</i>)-enoates proceeds with high diastereoselectivity to give the adducts having a stereogenic center with (<i>R</i>)-configuration at the β-position of the ester in the cyclopentene ring formation. The selectivity was reversed in the six-membered ring formation. On the other hand, the corresponding (<i>E</i>)-enoates provided Michael adducts with poor diastereoselectivity.