An efficient method for catalytic asymmetric allylic alkylation (AAA) of allylic phosphates with vinylaluminum reagents is reported. The vinylmetal reagents are prepared by reaction of commercially available DIBAL-H and a terminal alkyne. The resulting vinylaluminum reagent can be used directly, without isolation or purification. AAA reactions are promoted in the presence of 0.5−2.5 mol % of a readily available chiral N-heterocyclic carbene (NHC) complex and 1−5 mol % commercially available and air stable Cu salt (CuCl2·2H2O). The desired products are typically obtained within 2−12 h in 74% to 95% isolated yield, 77% to >98% ee, and in >98% E selectivity; >98% SN2‘ selectivity is obtained in all but one instance (90%). The hydroalumination/catalytic AAA sequence can be performed in a single vessel, on gram scale.
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The Pd(II)-catalyzed enantioselective organoboron-mediated Heck-type reaction is shown to proceed under molecular oxygen as an oxidant. The Pd(OAc) 2 /(S,S)-chiraphos catalyst gives good yield and the best enantioselectivity. Among the two possible d-and l-conformations in equilibrium, this reaction proceeds via the l-conformation of chiraphos with the two methyl groups in a diaxial orientation.
Optically active 3,3'-dimethyl-2,2'-diamino-1,1'-binaphthyl (DM-DABN) and 3,3'-dimethyl-2-amino-2'-hydroxybinaphthyl (DM-NOBIN) derivatives were synthesized by Cu-(-)-sparteine complex-catalyzed enantioselective homo- and hetero-coupling of 2-naphthylamine, respectively. The difference in enantioselectivity was observed by changing the concentration of oxygen.
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