Mono- and dialkylborane reagents from silylamine-boranes

Soderquist, John A.; Huertas, Ramon; Medina, Jesús R.

doi:10.1016/s0040-4039(98)01262-3

Cited by 21 publications

(7 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Only with the adduct 7 was the hydroboration of simple unhindered olefins is complete in 18 h, whereas, with the adducts 8 and 9 , the hydroborations were not complete even after 48 h at room temperature and the 11 B NMR studies showed the presence of starting amine−borane. This unusual rate retardation may be due to interaction of the solvent, dichloromethane, with the amine−borane, as reported earlier 7d…”

Section: Resultssupporting

confidence: 74%

See 1 more Smart Citation

Molecular Addition Compounds. 15. Synthesis, Hydroboration, and Reduction Studies of New, Highly Reactive tert-Butyldialkylamine−Borane Adducts

et al. 1999

View full text Add to dashboard Cite

Two series of tert-butyldialkylamines have been prepared and examined for borane complexation. The complexing ability of each amine in the two series examined decreases in the order shown. First series: t-BuN(CH2CH2)2O 1a > t-BuNEt2 1b > t-BuNPr n 2 1c > t-BuN(CH2CH2OMe)2 1d ≫ t-BuNBu i 2 1e. Second series: t-BuNBu i Me 2a > t-BuNPr i Me 2b > t-BuNBu i Et 2c > t-BuNBu i Prn 2d ≫t-BuNPr i Et 2e. The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. The following amines form highly reactive liquid borane adducts hydroborating 1-octene in tetrahydrofuran at room temperature in less than 1 h: t-BuN(CH2CH2OMe)2, t-BuNBu i Et, and t-BuNPr i Me. The limit of borane complexation among the amines examined is reached for t-BuNBu i 2 exchanging borane neither with BMS nor with BH3−THF. Among the various borane adducts prepared, the more promising borane adducts, t-Bu(CH3OCH2CH2)2N−BH3 (7), t-BuMePr i N−BH3 (8), and t-BuEtBu i N−BH3 (9), were selected for complete hydroboration and reduction studies. Hydroboration studies with the new, highly reactive trialkylamine−borane adducts 7−9 and representative olefins, such as 1-hexene, styrene, β-pinene, cyclopentene, norbornene, cyclohexene, 2-methyl-2-butene, α-pinene, and 2,3-dimethyl-2-butene, in tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane, and dichloromethane, at room temperature (22 ± 3 °C) were carried out. The reactions are faster in dioxane, requiring 1−2 h for the hydroboration of simple, unhindered olefins to the trialkylborane stage. Moderately hindered olefins, such as cyclohexene and 2-methyl-2-butene, give the corresponding dialkylboranes rapidly, with further slow hydroboration. However, the more hindered olefins, α-pinene and 2,3-dimethyl-2-butene, give stable monoalkylboranes very rapidly, with further hydroboration proceeding relatively slowly. The hydroborations can also be carried out conveniently in other solvents, such as THF, tert-butyl methyl ether, and n-pentane. A significant rate retardation is observed in dichloromethane. Regioselectivity studies of 1-hexene and styrene using these amine−borane adducts show selectivities similar to that of BH3−THF. The rates and stoichiometry of the reaction of t-BuMePr i N−BH3 in tetrahydrofuran with selected organic compounds containing representative functional groups were also examined at room temperature. The reductions of esters, amides, and nitriles, which exhibit a sluggish reaction at room temperature, proceed readily under reflux conditions in tetrahydrofuran and dioxane and without solvent (at 85−90 °C). The carrier amines can be recovered by simple acid−base manipulations in good yield and readily recycled to make the borane adducts.

show abstract

Section: Resultssupporting

confidence: 74%

“…The lower complexing ability of t -BuNEt 2 , as compared to N-tert- butylmorpholine suggested that substituting 2-methoxyethyl groups for ethyl groups might result in weaker borane complexation. Previously, it was also observed that diisopropyl(2-methoxyethyl)amine forms a weaker adduct with borane than did diisopropylethylamine …”

Section: Resultsmentioning

confidence: 97%

Molecular Addition Compounds. 15. Synthesis, Hydroboration, and Reduction Studies of New, Highly Reactive tert-Butyldialkylamine−Borane Adducts

et al. 1999

View full text Add to dashboard Cite

show abstract

“…Borane−amine adducts are widely encountered in modern synthetic organic chemistry and industrial processes . Notable examples of their applications include aqueous reductions of aldehydes and ketones, reductive aminations, olefin hydroborations, and amide reductions. 5b,c Recently, borane−amine adducts were employed in palladium-catalyzed systems such as epoxide openings, aryl triflate reductions, and N -alloc deprotections . Complexes of amine−boranes have also been utilized as chiral transfer agents, as activators for α-deprotonation of benzylamines, and as a protective device against nitrogen lone pair oxidation…”

mentioning

confidence: 99%

“…Usually, borane−amine complexes are readily formed by reduction of amides, imides, and imines or by treatment of the corresponding amine with diborane or borane carriers such as THF, DMS, and amines. , Tertiary amine−boranes have also been prepared from benzyl halides and lithium aminoborane (LAB) reagents . An attractive feature of these complexes is they are usually air-stable, crystalline compounds, and therefore are easily handled .…”

mentioning

confidence: 99%

Palladium and Raney Nickel Catalyzed Methanolic Cleavage of Stable Borane−Amine Complexes

et al. 2001

View full text Add to dashboard Cite

[figure: see text] Palladium and Raney nickel were found to catalyze the methanolysis of borane-amine adducts. Hence, strongly complexed amines can now be liberated by simple treatment with Pd/C or Raney Ni in methanol. The method is applicable to primary, secondary, tertiary, and aromatic amines, and the mildness of the reaction conditions allows preservation of otherwise labile functional groups.

show abstract

“…(+)-diisopinocampheylborane is prepared in high enantiomeric purity and good yield ( Table 1) by hydroboration of commercially available (−)-α -pinene (of low enantiomeric purity) with boranedimethyl sulfide (BMS) 5 or other reactive amine-boranes such as: tert-butyl-trimethylsilylamine-borane, 6 N-ethyl-Nisopropylaniline-borane (BACH-EI TM ) 7 , or N,N-diisopropyl-N-isobutylamine-borane. 8 Synthesis is carried out by mixing the α-pinene and borane complex in solvents such as dioxane (or THF) at 0 • C (eq 1).…”

mentioning

confidence: 99%