Borinates boronates from

We have used borylated water (water in which protons are replaced by BR2 groups) -so called organoboron water - in the reaction with aluminum alkyls. This works similarly but the reactions are more convenient. Apart from this organoboron water also some borinic, boronic or even boric acids have been used for this reaction. 

Borinic acids from boronic acid esters... 

A simple preparation of symmetrical and unsymmetrical borinic esters from selected boronic esters and organollthium reagents has... 

From Hard Allylic Organometallics. The most common preparation of allylic boranes and boronates is the addition of a reactive allylic metal species to a borinic or boric ester, respectively (Eqs. 10 and 11). Preparations from allyllithium, " " allylmagnesium, and allylpotassium " ° reagents are all well known. These methods are popular because the required allylic anions are quite easy to prepare, and because they generally lead to high yields of products. 

The addition of allylic boron reagents to carbonyl compounds first leads to homoallylic alcohol derivatives 36 or 37 that contain a covalent B-O bond (Eqs. 46 and 47). These adducts must be cleaved at the end of the reaction to isolate the free alcohol product from the reaction mixture. To cleave the covalent B-0 bond in these intermediates, a hydrolytic or oxidative work-up is required. For additions of allylic boranes, an oxidative work-up of the borinic ester intermediate 36 (R = alkyl) with basic hydrogen peroxide is preferred. For additions of allylic boronate derivatives, a simpler hydrolysis (acidic or basic) or triethanolamine exchange is generally performed as a means to cleave the borate intermediate 37 (Y = O-alkyl). The facility with which the borate ester is hydrolyzed depends primarily on the size of the substituents, but this operation is usually straightforward. For sensitive carbonyl substrates, the choice of allylic derivative, borane or boronate, may thus be dictated by the particular work-up conditions required. 

Lithium triethylcarboxide (1) is the base of choice for these conversions. The use of less hindered alkoxide or amide bases results in poorer yields. In this procedure 1.5-2.0 equivalents of base are required, although with more bulky alkyl groups attached to boron only 1 equivalent is necessary. The use of the more hindered 2,6-diisopropylphenol to form the borinic ester gives a 96% yield of the bicyclic ketone with only 1 equivalent of base however, in the work-up procedure this phenol is more difficult to separate from the ketone. 

Nucleophiles such as hydroxide or cyanide ion, in the presence of an oxidant, cause deboronation of ions (99) and (100) to give ion (96) and benzeneboronic acid. If no other oxidant is present the ions (99) and (100) themselves serve as oxidizing species to give a disproportionation. The use of mild reaction conditions stops the oxidation of (100) at the stage of (99). Nucleophiles like pyridine and hydride ion (from sodium borohydride) add to the borinate ring, pyridine to the boron atom and hydride to carbon atoms (79CB607). 

The boronic esters (Chart 9) are easily hydrolyzed to the corresponding homoallylic alcohols using triethanolamine 98). Consequently, the allylboration sequence provides a synthesically useful alternative to the familiar Grignard synthesis of homoallylic alcohols. However, the protonolysis by triethanolamine causes a problem in the isolation of homoallylic alcohol from the thick, sticky, air sensitive boron-containing mixture. Fortunately, treatment of a pentane solution of borinate esters of 9-BBN with 1-equivalent of ethanolamine results in the rapid formation of a fluffy white... 

A brief summary is included of carbohdyrate borinates—acyclic esters derived from borinic acids (R2BOH)—which have received less attention than the related boronates. 

It seems probable that a fundamental distinction may exist between the two methods available for the synthesis of carbohydrate boronates, in that, under dehydration conditions, esterifications may be reversible, whereas boronate formation from borinates is not. In the first, therefore, products may be thermodynamically controlled, whereas kinetic control will operate in the second. It is noteworthy, however, that products obtained from several glycopyranosides (a) by use of an ethylboronate derivative, and (b) by way of the per(diethylbor-inates) had the same structures.338... 

The reaction undergone by alcohols with trialkyl- and triaryl-boranes in the presence of pivalic acid, to give borinic esters, and the thermal cyclization of bis(dialkylborinates) to boronates, are discussed briefly in Section II. Many borinates have been prepared in quantitative yield from mono-, di-, oligo-, and poly-saccharides,338,108 and mixed... 

Significant features of these active borinic acid catalysts are that they are strong Lewis acids and have a hydroxy group on the boron atom. Dehydration is strongly favored in THF. The reaction usually proceeds smoothly, and a,/3-enones are obtained in high yields as ( ) isomers. In reactions of a-substituted-/3-hydroxy carbonyl compounds, a,/3-enones are preferentially obtained from anti aldols, whereas most syn aldols are recovered. This dehydration thus represents a useful and convenient method for isolating pure syn aldols from syn anti isomeric mixtures (Eq. 106). 

The reaction is not restricted to phosphorus, silicon, and boron compounds the tetrameric (NSEt) is, for instance, formed from ethylamine hydrochloride and sulfur dichloride (49). Nor is it restricted to nitrogen compounds the very stable cyclic phosphinoborines are formed by elimination of hydrogen from the dimethyl-phosphine borine complex (17). 

Although stereoselective formation of enolates from acyclic ketones with bases such as LDA is rather difficult, stereodefined boron enolates are more readily accessible. In the Mukaiyama method, an ethyl ketone is treated with a dialkylboron triflate and a tertiary amine, usually i-Pr2NEt. The resultant Z-(0) boron enolates (also known as enol borinates) are believed to be formed under kinetic control by deprotonation of the Lewis acid-complexed substrate. Brown and co-workers have shown that E- 0) boron enolates may be prepared by treatment of ethyl ketones with dicyclohexylboron chloride in the presence of Et3N. ... 

Borinic acids and their esters with the same or different alkyl, aryl or alkylaryl groups are conveniently prepared from organolithium reagents and selected boronic esters, e.g. ... 

Hydroboration of alkenes (185) with dibromoborane gives alkyldibromoboranes (186) which are easily converted into dioxaborinanes (187) (Scheme 25). These heterocycles also provide a convenient entry to aldehydes (189) through the addition of lithiated a-methoxy thioethers <83JA6285>. Unsym-metrical borinate esters (191) can be prepared from these boronates through the addition of organolithium compounds (cf. (190)) followed by treatment with acetyl chloride <850M1788,... 

Reaction C in Fig. 4 is an aldol condensation between an achiral aldehyde and an ester enol borinate featuring a bidentate chiral substituent at the boron atom [24]. Upon enolate-boron/aldehyde-oxygen co-ordination, two chair-like TS can be formed, both featuring the aldehyde phenyl group in a pseudo-equatorial position. Preferential attack on the aldehyde Si face is determined by the spatial arrangement of the metal ligand. The almost exclusive formation of the anti diastereoisomers arises from control of the enolate geometry. 

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