Boron-diol reaction

Boronate/diol reaction Chemical stimulation (e.g., sugar) [32]... 

Self-Assembly of Pol)miers Aided by Boron-Diol Reaction... 

Boron-Wittig reaction (12, 12-13). The direct reaction of the anion of an alkyldimesitylborane at -78° with an aromatic aldehyde followed by oxidation results in an (E)-alkene in low yield. The intermediate adduct can be isolated in about 80% yield as the silyl ether of a iyn-l,2-diol by addition of CISi(CH,), to the reaction, and this product on desilylation (HF, CHjCN) affords (E)-alkenes with high selectivity. Somewhat lower (E)-selectivity obtains in a one-pot reaction. In contrast, addition of trifluoroacetic anhydride (slight excess) to the reaction at -78° to -110° results in a (Z)-alkene with almost comparable selectivity (Z/E 9 1). 

Tertiary amines can serve as amine substrates for the boron-Mannich reaction, providing aromatic alkylation products of N,N-dialkyl-3-alkoxyanilines (Equation (125))573 and 1,3,5-alkoxy- or hydroxybenzenes (Equation (126)).574 The use of chiral diol esters of ( )-2-phenylethenylboronic acid for enantioselective alkylation resulted in 6-15% ee.575... 

In the synthesis of RK-397 (18), Denmark and Fujimori prepared an anft -diol using the Evans-Chapman-Carreira protocol5 (Scheme 4.2f). The (3-hydroxy ketone 21, obtained by a diastereoselective boron aldol reaction between 19 and 20, was reduced with tetramethylammonium triacetoxyborohydride to afford the anti-diol derivative 22 in greater than 19 ldiastereoselectivity. 

The molecular beacon fluorophore—quencher pairs methodology used in quantitative PCR (polymerase chain reaction) assays such as Taqman —may also be a useful signaling regime in the study of boron diol interactions. In appended quencher (Figure 10). 

On the basis of the simple boronic acid-diol reaction at the moleeular level, this chapter focuses on polymer-polymer interaetions triggered by boronic acid-diol esterification. When boronie aeid-diol reaetions oeeur cooperatively along a polymer chain, the structural changes caused by the complexation can easily amplify over hierarchies of nanometer to mierome-ter scale. Even without any signal such as fluorescence emission, the boronic acid-diol reaction based on precise molecular recognition is detectable as phase transition at the micrometer scale. 

Figure 9.1 Polymer-polymer interactions assisted by boronic acid-diol reaction (a) boronic acid-appended polymer-hydroxylated polymer interaction, (b) boronic acid-appended polymer-saccharide interaction, and (c) boronic acid-functionalized molecule-hydroxylated polymer...

Roush has crafted a class of allyl/vinyl diboron reagents that participate in sequential aldehyde addition 1,5-anti-diols reactions and enable the expeditious synthesis of 1,5-diols. The hydroboration reaction of allene 34 furnishes 35, treatment of which with aldehydes results in the formation of 36 (Scheme 5.6) [64]. These allylboronate adducts subsequently undergo addition to a second set of aldehydes, generating 1,5-anti-diols 37 with high diastereoselectivity (S 20 1) and optical purity (S 89% ee). Use of the bulkier boronate 38 gives 1,5-syn-diols 39 with equally high stereoselectivity (dr >14 1, ee>91%) [65]. 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

Studies have established that the partition between transition states 3 and 4 depends on the nature of the diol unit bound to boron and on the steric and electronic effects of the a-sub-stituent X23. The data shown below demonstrate that the reactions of2-(l-methyl-2-propenyl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane proceed with a moderate preference for transition state 3 with the C2 methyl group in an axial position. Selectivity diminishes with 2-(l-methyl-2-propenyl)-l,3,2-dioxaborolane and reverses with dimethyl (l-methyl-2-propenyl)boronale, suggesting that steric interactions (gauche interactions in the case of the tetramethyl-1,3,2-diox-aborolane) between X and the diol unit on boron are capable of destabilizing transition state 4 relative to 3. 

An interesting and stereoselective synthesis of 1,3-diols has been developed which is based on Lewis acid promoted reactions of /f-(2-propenylsilyloxy (aldehydes. Using titanium(IV) chloride intramolecular allyl transfer takes place to give predominantly Ag/r-l,3-diols, whereas anti-1,3-diols, formed via an / / /-molecular process, are obtained using tin(IV) chloride or boron trifluoride diethyl ether complex71. 

Crude chloroform-methanol-water (30 60 8, v/v) extracts of immunostainedTLC bands were analyzed without further purification by nanoelectrospray low-energy mass spectrometry. The authors showed that this effective PLC/MS-joined procedure offers a wide range of applications for any carbohydrate-binding agents such as bacterial toxins, plant lectins, and others. Phenyl-boronic acid (PBA) immobilized on stationary support phases can be put to similar applications. This technology, named boronate affinity chromatography (BAC), consists of a chemical reaction of 1,2- and 1,3-diols with the bonded-phase PBA to form a stable... 

Tetramethylammonium triacetoxyborohydride gives anft -l,3-diols from (3-hydroxy ketones.136 These reactions are thought to occur by a rapid exchange that introduces the hydroxy group as a boron ligand. 

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

It should be noted that one of these diols, the hydroquinone, did not provide any oligomer in the first step. This was due to the formation of the quinone structure which made it impossible to use hydroquinone directly in the substitution reaction. An alternate method was used to overcome this problem which involved the use of 4-methoxyphenol to obtain the sulfone product, followed by cleavage of the methyl ether to the diol (VIII) with boron tribromide. This set of reactions is outlined in Figure 5. 

Although this general principle of asymmetric induction has not been demonstrated for boron enolates, the related addition reactions of allylboranes to aldehydes (eq. [115]) (131) have been examined in this context. The reaction of chiral diol 175 with either triallyl-borane or tri- -methallylborane afforded the boronic esters 176 (Ri = H, Me) in yields exceeding 95% (132a). The addition reactions of 176 to representative aldehydes are summarized in Table 40. In all cases reported, the sense of asymmetric induction from the chiral... 

The weak nucleophilic nature of polynitroaliphatic alcohols is also reflected in their slow reactions with isocyanates to yield carbamates. These reactions often need the presence of Lewis acids like ferric acetylacetonate or boron trifluoride etherate. The reaction of bifunctional isocyanates with polynitroaliphatic diols has been used to synthesize energetic polymers.33°... 

The protected diol side-chain of 456 is introduced by asymmetric dihydroxylation and directs diastereoselectivity in the formation of 457 and 458 by lithiation. The most acidic position of 456, between the two methoxy groups, is first protected by silylation. Suzuki coupling of 459 with the boronic acid 460 gives the kinetic product 461—the more severe hindrance to bond rotation in this compound does not allow equilibration to the more stable atropisomer of the biaryl under the conditions of the reaction. 

Using 10% of DTBB as electron carrier, 2,5-disubstituted chlorocyclopentanes 6 were lithiated, the corresponding organolithium intermediates having being employed for the preparation of boronic esters 7, after reaction with triethyl borate and the corresponding 1,3-diol (Scheme 4). ... 

Tetrahydrofuran itself can be opened using either the stoichiometric or the catalytic version of arene-promoted lithiation, but both cases need the activation by boron trifluoride. The catalytic reaction was performed by treating the solvent THF 324 with the complex boron trifluoride-etherate and a catalytic amount (4%) of naphthalene. The intermediate 325 was formed. Further reaction with carbonyl compounds and flnal hydrolysis yielded the expected 1,5-diols 326 (Scheme 95), which could be easily cyclized to the corresponding substituted tetrahydropyrans under acidic conditions (concentrated FlCl). 

A mild one-pot procedure based on a platinum-catalyzed diborylation of 1,3-butadienes (see Eq. 30) gives doubly allylic boronate 144, which adds to an aldehyde to form a quaternary carbon center in the intermediate 145 (Eq. 105). The use of a tartrate auxiliary in this process leads to good levels of enantiose-lectivity in the final diol product, which is obtained after oxidation of the primary alkylboronate intermediate. Although examples of aliphatic, aromatic, and unsaturated aldehydes have been described, enantioselectivities vary widely (33 to 74% ee), and are good only for aliphatic aldehydes. An intramolecular variant of this interesting tandem reaction is also known. ... 

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