2,3-Dimethyl-2-butylborane

Monosubstituted Boranes. Only a few monoaLkylboranes are directiy available by hydroboration. Tertiary hexylborane, 2,3-dimethyl-2-butylborane [3688-24-2] (thexylborane, Thx) BH2 (5), easily prepared from 2,3-dimethyl-2-butene, is the best studied (3,60—62). It should be... 

On the other hand, the observed syn preference of 59a is consistent with a study of hydroboration of 59a with diborane by Schueler and Rhodes [127], who obtained a mixture of the monoalcohols (symanti = 74 26) upon oxidative work-up. A similar magnitude of. yyn-preference was found (syn anti = 73 27) in the hydroboration with a bulkier borane, 2,3-dimethyl-2-butylborane (thexyl borane) [127]. This lack of effect of the bulk of the reagent in the hydroboration of 59a is consistent with the idea that the n face of 59a is free from steric bias [127], and that the syn preference of 59a found in dihydroxylation and epoxidation is non-sterically determined [128]. 

It is clear from these representative results that regioselectivity in hydroboration is controlled by steric effects. As a result, nonsymmetric internal olefins usually yield a mixture of regioisomeric alkylboranes when they react with borane. Several hindered mono- and diakylboranes with sterically demanding alkyl groups, however, have been developed for use in selective hydroboration. Disiamylborane [bis(3-methyl-2-butyl)borane, 34], thexylborane (2,3-dimethyl-2-butylborane, 35), and 9-BBN (9-borabicyclo[3.3.1]nonane) are the most frequently used reagents. Improvements of regioselectivities in hydroboration of both... 

Special methods are required for the direct reduction of RC02H to RCHO. Aldehydes can be obtained directly by the slow reduction of carboxylic acids with 2,3-dimethyl-2-butylborane in oxacyclopentane solution. 

Direct reduction of aldehydes with 2,3-dimethyl-2-butylborane proceeds rapidly and gives the corresponding alcohol. Nonetheless, reduction of carboxylic acids with the same borane (Section 18-3C) proceeds slowly and gives high yields of aldehydes. Explain why the reaction of RC02H with the 2,3-dimethyl-2-butylborane produces RCHO instead of RCH2OH. 

Addition of borane to 2,3-dimethylbut-2-ene gives 2,3-dimethyl-2-butylborane (thexylborane) which is also a synthetically useful substituted borane. 

HYDROBORATION, REAGENTS His-(3,6-dimethyl)borepane. Bix(3,5-dimeth-yl)borinane. Bis((rans-2-methylcydo-hesyOborane. Catceholborane. Diborane. Dichloroborane diethyl etherate. Dicyclo-hexylborane. Diisopinocamphenoborane. 2,3-Dimethyl-2-butylborane. Monochloro-borane-Ethyl etheiate. 

HYDROBORATION Bis(3,6-dimethyl)bore-pane. Bis(trans-2-methylcyclohexyl)bo-rane. Catecholborane. Dicyclohexylbo-rane. Diisopinocamphenylborane. 2,3-Dimethyl-2-butylborane. Dimethyl sul-fide-Borane. Monochloroborane-Diethyl etherate. 

As noted above, the hindered 2,3-dimethyl-2-butene (1) reacts with diborane (1-2 hrs. in digylme) to give the monoalkyl borane (2), 2,3-dimethyl-2-butylborane... 

Carbonylation of organoboranes Carbon monoxide. N,N -Carbonyl-diimidazole. 2,3-Dimethyl-2-butylborane. Hydrogen fluoride—Antimony pentafluoride. Lithium trimethoxyaluminum hydride. Palladium (II) chloride. 

Annelation l,3-Dichloro-2-butene. 2,3-Dimethyl-2-butylborane. 3,5-Dimethyl-4-chloro-methylisoxazole. Methyl vinyl ketone. (rons-3-Pentene-2-one. Pyrrolidine. 

The ease of dehydroboration of alkylboranes decreases in the order tertiary > secondary > primary. The order of the ease of hydroboration is opposite to this. Both factors contribute to the order of isomerization decreasing tertiary > secondary > primary. Isomerization of sterically hindered or strained alkylboranes may occur even at RT e.g., oxidation of freshly prepared 2,3-dimethyl-2-butylborane (thexylborane) gives a 99 1 mixture of 2,3-dimethyl-2-butanol and 2,3-dimethyl-1-butanol, whereas oxidation... 

ALKENES Allyl dimethyldithiocarbamate. Bis(t -cyclopentadienyl)niobium trihydride. Cyanogen bromide. Di-n-butylcopperlithium. a,o-Dichloromethyl methyl ether. 2,3-Dimethyl-2-butylborane. N,N-Dimethyl dichlorophosphoramide. Diphenyl diselenide. Di-n-propylcopperlithium. Ferric chloride. Grignard reagents. Iodine. Lithium phenylethynolate. Lithium 2,2,6,6-tetramethylpiperidide. Methyl iodide. o-Nitro-phenyl selenocyanate. Propargyl bromide. rra s-l-Propenyllithium. Selenium. Tetrakis(triphenylphosphine)palladium. Titanium(IH) chloride. Titanium trichloride-Lithium aluminum hydride. p-Toluenesulfonylhydrazine. Triphenylphosphine. Vinyl-copper reagents. Vinyllithium. Zinc. 

Dimelhyl-2-butene added at 0° to 3.1 M borane in tetrahydrofuran to form thexylborane (2,3-dimethyl-2-butylborane), stirring continued 1 hr. at 0°, a soln. of isobutylene in tetrahydrofuran added and allowed to react 0.5 hr. at 0°, then ethyl vinylacetate added, allowed to stand 2 hrs. at 0°, water added, kept 3 hrs. at 50° under 70 atm. GO in a stainless-steel autoclave, transferred to a glass flask, 3 M Na-acetate added followed by O -HgOg at a rate to maintain the temp, at 30-40°, and kept 1 hr. at 50° — ethyl 7-methyl-5-oxooctanoate. Y 84%. - Because of the low migration aptitude of the thexyl group, either the same or two different olefins with a wide variety of functional groups can... 

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