The catalytic asymmetric 1,4-addition of thiols to cyclic enones with modified cinchona alkaloid has been demonstrated (Scheme 3). The Michael products can be isolated with high yield and enantioselectivity for a range of substances.

Scheme 3. Enantioselective Michael Addition of Thiophenols to Enones

Later, tandem Michael-aldol reactions have been developed for the preparation of medicinally important chiral thiochromanes (Scheme 4). This new one-pot process proceeds with 1 mol % of the cinchona alkaloid derived thiourea catalyst L2 , which synergistically activates both the Michael donor and acceptor.

Scheme 4. Reaction of 2-Mercaptobenzaldehyde with α,β -Unsaturated oxazolidinone

Similarly, the conjugate addition has been reported with catalyst L3 for a direct, stereocontrolled construction of adjacent carbon- or heteroatom-substituted quaternary and tertiary stereocenters from readily available starting β -ketoester (Scheme 5).

Scheme 5. Asymmetric Michael Addition Reaction