Axial N-O alcohols, which have two large carboline moieties connected to the axis were synthesized and used in catalytic enantioselective 1,2-and 1,4-transfer hydrogenations of total 26 ketimines and β-enamino esters. Excellent levels of enantioselectivity ranging from 91% to 99% were achieved by using catalyst (aS)-2oxide. Interestingly, a mixture of (aS)-(S)-3,3'-bis ((S)-2-(hydroxymethyl)pyrrolidine-1-carbonyl)-9,9'dimethyl- 9H,9'H-[1,1'-bipyrido[3,4-b]indole] 2oxide and (aR)-(S)-3,3'-bis((S)-2-(hydroxymethyl) pyrrolidine-1-carbonyl)-9,9'-dimethyl-9H,9'H-[1,1'bipyrido[3,4-b]indole] 2-oxide was also able to provide high enantioselectivities up to 95% that is the same as that using pure (aS)-(S)-3,3'-bis((S)-2-(hydroxymethyl)pyrrolidine-1-carbonyl)-9,9'dimethyl- 9H,9'H-[1,1'-bipyrido[3,4-b]indole] 2oxide. A plausible catalytic mechanism was suggested and total four kinds of transition states (TS) including almost 60 TS structures were investigated using density functional theory (DFT) with different basis sets such as 6-311G(2d,p). The predicted activation energy data are consistent with the experimental results.

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This mechanistic study demonstrates that an unusual h 1 -coordinated alkyne complex is criticalf or the 1-pentyne 1,1-diboration reaction. The comparatives tudies suggest the "pull-push" antagonistic effect arising from Lewis acidity and steric congestion as the reason for the existence of h 1 -coordinated alkyne complexes. Analogous h 1 -coordinated alkene complexes are also predicted and seem to be promising for their applicationt ot he important olefin polymerization reaction.Scheme1.Synthesis of 1,1-and 1,2-diboration of 1-pentyne by Erker and co-workers. [8] [a] Dr.

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