Boranes hydrolysis

Reduction of phenols 5-12 Oxidation of boranes hydrolysis of unsaturated boranes... 

Lithium trialkylalkynyl borates react in a stereoselective manner with benzo-dithiolithium tetrafluoroborate to give vinyl boranes. Hydrolysis of the vinyl boranes, the rate of which differs significantly for the E and Z-isomers gives protected unsaturated aldehydes (Scheme 25). 

Kalidindi, S. B. Indirani, M. Jagirdar, B. R., First row transition metal ion-assisted ammonia-borane hydrolysis for hydrogen generation, Inorg. Chem. 2008, 47, 7424-7429. 

Basu, S. Brockman, A. Gagare, P Zheng, Y Ramachandran, P. V. Delgass, W. N. Gore, J. P., Chemical kinetics of Ru-catalyzed ammonia borane hydrolysis, J. Power Sources 2009,188, 238-243. 

Diborane or aUcylboranes are used for reduaion of alkenes and alkynes via hydrobora-tion (see pp. 37f., 47f., 130f.) followed by hydrolysis of the borane with acetic acid (H.C. Brown, 1975). 

The triaLkoxy(aryloxy)boranes are typically monomeric, soluble in most organic solvents, and dissolve in water with hydrolysis to form boric acid and the corresponding alcohol and phenol. Although the rate of hydrolysis is usually very fast, it is dependent on the bulk of the alkyl or aryl substituent groups bonded to the boron atom. Secondary and tertiary alkyl esters are generally more stable than the primary alkyl esters. The boron atom in these compounds is in a trigonal coplanar state with bond hybridization. A vacantp orbital exists along the threefold axis perpendicular to the BO plane. 

N HCl) are necessary for the hydrolysis of The [B22H22] anion is the most hydrolytically stable borane anion, withstanding even 3 NUCl... 

The influence of boron-bonded ligands on the kinetics and mechanistic pathways of hydrolysis of amine boranes has been examined (37,38). The stoichiometry of trimetbyl amine azidoborane [61652-29-7] hydrolysis in acidic solution is given in equation 10. It is suggested that protonation occurs at the azide ligand enabling its departure as the relatively labile HN species. 

Boronic acids RB(OH)2 were first made over a century ago by the unlikely route of slow partial oxidation of the spontaneously flammable trialkyl boranes followed by hydrolysis of the ester so formed (E. Frankland, 1862) ... 

Trialky I boranes react rapidly with methyl vinyl ketone (and other a,j8-unsaturated ketones) to yield, after hydrolysis, methyl ketones of the indicated structure 4). The reaction with acrolein is analogous to give jS-alkylpropionaldehydes (5). The process is inefficient in that only one of the three alkyl groups of the borane is converted into product, but the rapidity and ease of carrying out the reaction may be adequate... 

Hydrolysis of 1-boronylallylstannanes, available by stannylation of alkenyl and allyl boranes. gives (Z)-allylstannanes stereoselectively34. 

No matter which of the electrophilic methods of double-bond shifting is employed, the thermodynamically most stable alkene is usually formed in the largest amount in most cases, though a few anomalies are known. However, there is another, indirect, method of double-bond isomerization, by means of which migration in the other direction can often be carried out. This involves conversion of the alkene to a borane (15-16), rearrangement of the borane (18-11), oxidation and hydrolysis of the newly formed borane to the alcohol (12-28), and dehydration of the alcohol (17-1) ... 

An indirect method ° of double-bond reduction involves hydrolysis of boranes (prepared by 15-16). Trialkylboranes can be hydrolyzed by refluxing with carboxylic acids,while monoalkylboranes RBH2 can be hydrolyzed with base. ° Triple bonds can be similarly reduced, to cis alkenes. °... 

Catalytic hydrogenation of triple bonds and the reaction with DIBAL-H usually give the eis alkene (15-11). Most of the other methods of triple-bond reduction lead to the more thermodynamically stable trans alkene. However, this is not the case with the method involving hydrolysis of boranes or with the reductions with activated zinc, hydrazine, or NH2OSO3H, which also give the cis products. 

Alkylation and hydrolysis of imines alkylation of aldehydes 10-107 Alkylation and hydrolysis of dithianes 10-108 Alkylation and hydrolysis of oxazines and similar compounds 10-109 Reaction of diazo aldehydes with boranes... 

The Leuckart-Wallach reaction is the oldest method of reductive amination of carbonyl compounds. It makes use of formamide, formic acid or ammonium formate at high temperature. The final product is a formamide derivative, which can be converted to an amine by reduction or hydrolysis. The method has been applied to the preparation of 1,2-diamines with a norbornane framework, which are interesting rigid analogues of 1,2-diaminocyclohexanes. As a matter of fact, starting from N-acetyl-2-oxo-l-norbornylamine 222, the diamide 223 was obtained with excellent diastereoselectivity and then converted to the M-methyl-N -ethyl derivative 224 by reduction with borane [ 104] (Scheme 34). On the other hand, when the reac-... 

Also, desymmetrization of prochiral hydroxyalkylphosphine P-boranes was successfully performed using similar reagents and conditions. In the case of bis(hydroxymethyl)phenylphosphine P-borane 87, both its acetylation and hydrolysis of the diacetyl derivative 89 gave good results, although in addition to the expected monoacetate 88, the diol 87 and diacetate 89 were always present in the reaction mixture (Equation 42). °°... 

Several alternative procedures have been developed in which other reagents replace carbon monoxide as the migration terminus.11 The most generally applicable of these methods involves the use of cyanide ion and trifluoroacetic anhydride (TFAA). In this reaction the borane initially forms an adduct with cyanide ion. The migration is induced by N-acylation of the cyano group by TFAA. Oxidation and hydrolysis then give a ketone. 

The formation of a strong intramolecular dative P—B bond in the hydro-borylation reaction of diallylphenylphosphine with triethylaminophenyl-borane results in a bicyclic product, l-borata-5-phosphoniabi-cyclo[3,3,0]octane (204) [Eq. (145)] (64JA5045). The presence of the dative bond in this compound is indicated by an NMR study and by its stability to hydrolysis and oxidation. 

The first example of allylation of imines using dialkyl 2-allyl-l, 3-dioxaborolane-4,5-dicarboxylates 110 or fi-allyldiisopinocamphcnyl borane 154 was reported in 1995." After hydrolysis of the reaction product, homoallyl primary amine was obtained in 54-90% yield and up to 73% ee (Scheme 3-52). 

Brown proposed a mechanism where the enolate radical resulting from the radical addition reacts with the trialkylborane to give a boron enolate and a new alkyl radical that can propagate the chain (Scheme 24) [61]. The formation of the intermediate boron enolate was confirmed by H NMR spectroscopy [66,67]. The role of water present in the system is to hydrolyze the boron enolate and to prevent its degradation by undesired free-radical processes. This hydrolysis step is essential when alkynones [68] and acrylonitrile [58] are used as radical traps since the resulting allenes or keteneimines respectively, react readily with radical species. Maillard and Walton have shown by nB NMR, ll NMR und IR spectroscopy, that tri-ethylborane does complex methyl vinyl ketone, acrolein and 3-methylbut-3-en-2-one. They proposed that the reaction of triethylborane with these traps involves complexation of the trap by the Lewis acidic borane prior to conjugate addition [69]. 

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