Catalytic conjugate addition promoted by the copper(I)–monothiobinaphthol system. Part 2.1 Optimal ligand synthesis and initial catalytic results

Abstract

Both racemic and (R_a)-1,1′-bi-2-naphthol react with Bu₂SnO to provide an O,O-stannylene acetal which opens with Me₂NC(S)Cl or RC(O)Cl [R = Ph, CCl₃, OPr, 1-C₁₀H₇, 2-C₁₀H₇, SMe, CH₂Cl and (-)-menthyl] to fashion monoacylated derivatives. Two of the products, 2-(N,N-dimethylthiocarbamoyloxy)-2′-hydroxy-1,1 ′-binaphthyl 6 and 2-hydroxy-2′-[(1R,3S,5R)-menthylcarbon yloxy]-1,1′-binaphthyl 14, have been crystallographically characterised. The former is converted to 2-(N,N-dimethylcarbamoyloxy)-2′-(N, N-dimethylthiocarbamoyloxy)-1,1′-binaphthyl 15 with Me₂NC(O)Cl. This compound is directly available from 1,1′-bi-2-naphthol via a one-pot sequential reaction with Me₂NC(S)Cl and Me₂NC(O)Cl under NEt₃–DMAP catalysis. Thermolysis of 15 followed by hydrolysis provides an efficient preparation of 2-hydroxy-2′-mercapto-1,1′-binaphthyl 3 (monothiobinaphthol). In the presence of [Cu(MeCN)₄]BF₄, 3 leads to a highly efficient catalyst for the 1,4-addition of BuLi and RMgX (R = Me, Bu, Ph; X = Cl, Br) to cyclic enones.