Thexyl- And Isopinocampheylhaloboranes as Stereoselective Reducing Agents

Soon, Jin; Min, Soo Jin; Kim, Jong Mi; Kwon, Oh Oun; Jeoung, M. K.

doi:10.1080/00304949309457991

Cited by 9 publications

(8 citation statements)

References 5 publications

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“…We applied the same technique for the hydroboration-oxidation of fluoro-substituted styrenes (Scheme 4). Thus, the hydroboration of 4-fluorostyrene with BH 2 IÁSMe 2 , prepared via the iodination [18] of BH 3 ÁSMe 2 in CS 2, was complete within 5 h at RT, as revealed by a doublet at d À6.5 in the 11 B NMR spectrum. The reaction mixture was cooled to 0 8C, quenched with methanol and oxidized under alkaline conditions to obtain a 95 % yield of essentially pure primary alcohol product 3c (3c:5c = 97:3).…”

Section: Resultsmentioning

confidence: 96%

Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Ramachandran

Madhi

O’Donnell

2006

Journal of Fluorine Chemistry

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Section: Resultsmentioning

confidence: 96%

Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Ramachandran

Madhi

O’Donnell

2006

Journal of Fluorine Chemistry

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“…Recently, Cha et al have reported the hydroboration of α-pinene with methyl sulfide complexes of monohaloboranes (BH 2 X·SMe 2 ; X = Cl, Br, and I) to provide methyl sulfide complexes of isopinocampheylhaloboranes (IpcBHX·SMe 2 ; X = Cl, Br, and I). However, there is no mention of the purity of these reagents, or their applicability for asymmetric hydroboration.…”

Section: Resultsmentioning

confidence: 99%

“…However, there is no mention of the purity of these reagents, or their applicability for asymmetric hydroboration. In view of our program in asymmetric synthesis via organoboranes using sterically varied pinene-based chiral auxiliaries 7-9 and also the potential of IpcBHCl ( 3 ) for further synthetic manipulations, we undertook a systematic study of its synthesis by various promising approaches: (1) by the direct hydroboration of α-pinene with monochloroborane dimethyl sulfide (BH 2 Cl·SMe 2 ); (2) the reaction of IpcBH 2 with HCl; (3) exchange of IpcBH 2 with IpcBCl 2 ; (4) reduction of IpcBCl 2 with Me 3 SiH; and (5) reduction of IpcBCl 2 with 1/4 equiv of LAH. We also examined the effect of solvents, such as pentane, CH 2 Cl 2 , EE, and THF, in methods (3) and (4) to provide pure IpcBHCl.…”

Section: Resultsmentioning

confidence: 99%

Hydroboration. 92. Investigation of Practical Methods for the Synthesis of Optically Pure Isopinocampheylchloroborane for the Asymmetric Hydroboration of Representative Prochiral Alkenes

1996

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A quantitative study was made of the preparation of the optically pure borane reagent, isopinocampheylchloroborane (IpcBHCl), potentially valuable for asymmetric hydroboration. IpcBHCl (87−90%) in equilibrium with 5−6.5% of IpcBCl2 and IpcBH2, respectively, can be prepared conveniently by a number of relatively simple operations: (1) the reaction of isopinocampheylborane (IpcBH2) with anhydrous hydrochloric acid (HCl) in ethyl ether (EE); (2) the reaction of stoichiometric amounts of IpcBH2 with isopinocampheyldichloroborane (IpcBCl2) in EE; and (3) the reduction of IpcBCl2 with trimethylsilane (Me3SiH) or lithium aluminum hydride (LAH) in EE. The reduction of IpcBCl2 with Me3SiH in pentane proceeds extremely slowly to provide the desired reagent, IpcBHCl. However, in EE, the reduction proceeds much faster, providing an equilibrium mixture of 90% IpcBHCl, 5% IpcBH2, and 5% IpcBCl2. We also investigated the reduction of IpcBCl2 with Me3SiH in pentane and dichloromethane (CH2Cl2) in the presence of known amounts of EE, tetrahydrofuran (THF), and dimethyl sulfide (SMe2), solvents which coordinate with the dichloroboranes. A comparative study of the rate of hydroboration of the alkene, 2-methyl-2-butene, with IpcBH2 and IpcBHCl, obtained as described above, was made in representative solvents, such as pentane, CH2Cl2, EE, and THF, at 0 °C and, in many cases, also at 25 °C. This study revealed that the rate of hydroboration is faster in THF for IpcBH2, while for IpcBHCl, the rate is faster in EE. Asymmetric hydroboration of prochiral alkenes was achieved by two methods, viz., IpcBHCl, produced by the reaction of IpcBH2 with HCl in EE (method A), and the reduction−hydroboration reaction of IpcBCl2 with LAH (0.25 equiv) in the presence of the prochiral alkene (method B) in EE. In both methods, the temperature of the reaction mixture was maintained at −25 °C. Almost identical results were realized in these two procedures, with the enantiomeric excess (ee) realized with IpcBHCl, in some cases, considerably better than that achieved with IpcBH2. Although, IpcBHCl was obtained in only 87−90% purity along with IpcBH2 and IpcBCl2 as side products, the presence of the latter compound had no observable effect on the chiral outcome of the asymmetric hydroboration.

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“…As mentioned earlier, diisobutylaluminum derivatives (17)(18)(19)(20)(21)(22)(23) 114, 122,124,125,126,140,[144][145][146][147][148] and diisopinocampheylboron derivatives (25)(26)(27)(28)(29)(30)(31)(32)(33) 132, [135][136][137]140,[149][150][151][152][153] have been applied to the regioselective reduction of α,β-unsaturated aldehydes and ketones. All the derivatives examined can reduce a variety of α,β-unsaturated aldehydes and ketones to the corresponding allylic alcohols, except Ipc 2 BOR 135-138, which can only reduce aldehydes but not attack ketones at all.…”

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confidence: 99%

“…Isopinocampheylhaloboranes. Isopinocampheylhaloboranes-methyl sulfide (IpcBHX·SMe 2 , X=Cl, Br, I) can be prepared by the hydroboration of α-pinene with the corresponding H 2 BX·SMe 2 (X=Cl, Br, I) in methylene chloride 22,23 (Eq. 17).…”

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confidence: 99%

Thirty Six Years of Research on the Selective Reduction and Hydroboration

Soon¹

2011

Bulletin of the Korean Chemical Society

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thirty six years, the author and his collaborators have developed a variety of reducing and hydroborating agents, and applied them to organic synthesis, which involves the 1,2-reduction of α,β-unsaturated carbonyl compounds, stereoselective reduction of cycloalkanones, regioselective ring-opening of epoxides, partial reduction of carboxylic acid derivatives to aldehydes, regioselective addition to carbon-carbon multiple bonds, etc. by utilizing metal hydrides and the newly-devised the Meerwein-Ponndorf-Verley (MPV) type reagents. Such developments provide a new synthetic methodology making possible valuable selective reductions and hydroborations, not practical previously.

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Thexyl- And Isopinocampheylhaloboranes as Stereoselective Reducing Agents

Cited by 9 publications

References 5 publications

Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Hydroboration. 92. Investigation of Practical Methods for the Synthesis of Optically Pure Isopinocampheylchloroborane for the Asymmetric Hydroboration of Representative Prochiral Alkenes

Thirty Six Years of Research on the Selective Reduction and Hydroboration

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