Catalytic conjugate addition promoted by the copper(I)-monothiobinaphthol system. Part 3. Comparison of three thiolate-based catalytic systems

Monothiobinaphthol (MTB, 2-hydroxy-2'-mercapto-1,1'-binaphthyl undergoes S- alkylation with BuBr and alpha,omega-dihalides to afford thioether species. The precursor to MTB, 2-(N,N-dimethylcarbamoyloxy)-2'-(N,N-dimethylcarbamo ylthio)- 1,1'-binaphthyl, undergoes anionic Fries rearrangement of the O-ar yl carbamate to afford a crystallographically characterised amido species. Hydrolysis of this species affords the 3-C(O)NMe2 analogue of MTB. These MT B-based ligand systems have been tested in asymmetric conjugate addition re actions of cyclic and acyclic enones and compared with 1,1'-bi(2-thionaphth ol). Active catalysts are formed in all cases but only low enantioselectivi ties are realised (0-55% ee). Full conditions for the separation of the ena ntiomeric conjugate addition products are reported.