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

Abstract

Monothiobinaphthol (MTB, 2-hydroxy-2′-mercapto-1,1′-binaphthyl undergoes S-alkylation with BuBr and α,ω-dihalides to afford thioether species. The precursor to MTB, 2-(N,N-dimethylcarbamoyloxy)-2′-(N,N-dimethylcarbamoylthio)-1,1′-binaphthyl, undergoes anionic Fries rearrangement of the O-aryl carbamate to afford a crystallographically characterised amido species. Hydrolysis of this species affords the 3-C(O)NMe₂ analogue of MTB. These MTB-based ligand systems have been tested in asymmetric conjugate addition reactions of cyclic and acyclic enones and compared with 1,1′-bi(2-thionaphthol). Active catalysts are formed in all cases but only low enantioselectivities are realised (0–55% ee). Full conditions for the separation of the enantiomeric conjugate addition products are reported.