| Research Abstract |
1. Catalytic C-H Borylation
Direct C-H borylation of arenes catalyzed by a transition metal complex was studied as an economical protocol for the synthesis of a variety of arylboron derivatives. Ir-catalyzed C-H borylation of arenes, heteroarenes, and benzylic positions of alkylarenes by bis(pinacolato)diboron or pinacolborane furnished aryl-, heteroaryl-, and benzylboron compounds.
2. Catalytic Hydroboration
Hydroboration of terminal and internal alkenes with pinacolborane or N, N', N"-trimethyl-and N, N', N"-triethylborazine was carried out at 25-50℃ in the presence of rhodium(I) or iridium(I) catalyst.
Addition of dppb or DPEphos to RhH(COXPPh_3)_3 gave the best catalyst for hydroboration of ethylene at 50℃, resulting in a quantitative yield of B, B', B"-triethyl-N, N', W-trimethylborazine. On the other hand, a complex prepared from (t-Bu)_3P and [Rh(coe)_2Cl]_2 gave the best yield for hydroboration of terminal or internal alkenes.
3, 5, 6. Rhodium and Palladium Catalyzed Addition Reactions of Organoboron compounds.
An enantioselective synthesis of cyclic and acyclic P-aryl ketones and esters via palladium(II)-or rhodium(I)-catalyzed 1,4-addition of Ar-[m] (m=B(OH)_2, BF_3K, Si(OMe)_3, SiF_3, BiAr_2) to α, β-unsaturated ketones or esters is described. The enantioselection mechanism and efficiency of a chiraphos ligand for structurally planar α, β-unsaturated ketones are discussed on the basis of the X-ray structure of the catalyst and results of DFT computational studies on the modes of coordination of the substrates to the phenylrhodium(I)/(S, S)-chiraphos intermediate.
4. Catalytric Allylboration
The asymmetric cross-coupling reaction of [CH_3CH=CHCH_2BF_3]K with aryl or 1-alkenyl bromides selectively occurred at the γ-carbon of 2-butenylborane moiety with regioselectivities in a range of 84-99%. The enantioselectivities were in a range of 77-90%ee when a palladium/CyPF-t-Bu complex was used at 80℃ in the presence of K_2CO_3 in H_2O-MeOH (9/1).
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