Electrosynthesis of boronic acids and esters

Electrosynthesis offers an interesting alternative to the classical synthesis of organoboronic derivatives. Aryl-, allyl- and benzylboronic acids can be prepared via the reduction of organic halides in the presence of trialkylborates or pinacolborane. Electrochemical methodology avoids the use of noble metals and of low temperatures. It also allows the use of more accessible organic chlorides as starting substrates. With dihalogenated derivatives, good borylation selectivities can be obtained.

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Homologation of boronic esters with trimethylsilylchloromethyllithium

Trimethylsilylchloromethyllithium adds to boronic esters to form ate complexes which rearrange with displacement of chloride to form the homologous α-trimethylsilyl boronic esters in high yields.     

Facile preparation of thiol esters from organotin mercaptides and acyl chlorides

Organotin mercaptides condense with acyl chlorides to give thiol esters in excellent yield. Of note are efficient syntheses of $\text{t}$-butyl and phenyl thiol esters.     

雪松烷二醇硼酸酯的合成及其不对称同系化反应

报道了手性试剂雪松烷二醇硼酸酯(3)的合成及其和二氯甲基锂进行不对称同系化反应,生成α-氯代硼酸酯4R和4S,其R/S的比率在25:1以上,并且有手性助剂容易回收的特点。通过对同系化产物4cR的单晶X衍射分析,发现其分子中的1,3-二氧杂-2-硼杂环戊烷为非平面结构,文中就这一结构特点进行了初步讨论,解释了雪松烷二醇硼酸酯容易水解的原因。     

Suzuki-Miyaura cross-couplings of secondary allylic boronic esters

Palladium-catalyzed cross-coupling reactions of secondary allylic boronic esters with iodoarenes were demonstrated under the conditions previously described for the coupling of benzylic substrates. The regioselectivity of the process was largely dictated by the pattern of olefin substitution.     

(1-Methoxyvinyl)boronic and (1-chlorovinyl)boronic esters

(s)-Pinanediol (1-methoxyvinyl)boronate ( 1 ) was prepared from (1-methoxyvinyl)-lithium and triisopropyl borate followed by (s)-pinanediol. Attempted reaction with (dichloromethyl)lithium failed, and reaction with butylmagnesium chloride followed by acetic acid yielded a mixture of diastereomers of (s)-pinanediol (1-methoxy-1-methyl-pentyl)boronate ( 2 ). (s)-Pinanediol (1-chlorovinyl)boronate ( 4 ) has been prepared by dehydrochlorination of (s)-pinanediol 1,1-dichloroethylboronate ( 3 ) with lithium chloride in dimethylformamide. Reaction of 4 with (dichloromethyl)lithium yielded (s)-pinanediol (1S)-(1,2-dichloroallyl)boronate ( 5 ) in 92% diastereomeric excess. Reaction of 5 with RMgX resulted in a 3 : 1 ratio of displacement of the 1-Cl from carbon by R to displacement of the entire 1,2-dichloroallyl group from boron by R. With lithium benzyl oxide, displacement of the 1-Cl from 5 failed entirely. Reaction of 4 with (dibromomethyl)lithium was inefficient and yielded a gross mixture of diastereomers.     

A borylative cyclisation towards indole boronic esters

2-Alkynylaniline borylative cyclisations provide a direct means to access indole 3-boronic esters from simple precursors. The Pd-catalysed cyclisation can be merged with cross-coupling processes in the same reaction vessel, moreover, the products can be exploited in C-N bond forming reactions.     

FeCl3-mediated synthesis of fullerenyl esters as low-LUMO acceptors for organic photovoltaic devices

C(60) reacted with aromatic and aliphatic carboxylic acids in the presence of inexpensive FeCl(3) at room temperature to produce hydroxyfullerenyl esters C(60)(OCOR)(OH) in up to 68% isolated yield. The hydroxyl group was utilized in functional group transformations to obtain a diester derivative C(60)(OCOAr)(OCOPh) (Ar = 2,6-xylyl) and a siloxyl derivative C(60)(OCOAr)(OSiMe(3)). The diester and siloxyl derivatives were found to possess low-lying LUMO levels were utilized in organic photovoltaic devices showing 1.3% power conversion efficiency.     

Facile and effective approach for oxidation of boronic acids

This present work illustrates facile and effective approach for oxidation of boronic acids using environmentally benign dimethyl carbonate (DMC) as a solvent with H₂O₂ as an oxidant at room temperature. In contrast to previous reaction reports, which make use of metal catalyst, hazardous reagent and oxidants that creates environmental concern. This method provides good to excellent yield of products and showed better tolerance towards various functional groups present on boronic acids. Moreover, this developed process is an alternative in terms of inexpensive, non toxic and easy reaction conditions.     

Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters

(Azidomethyl)boronic esters of 1,2-dicyclohexyl-1,2-ethanediol (“DICHED”) and pinanediol have been prepared from the corresponding (bromomethyl)boronic esters. Conversion to (2-azido-1-chloro- or bromoethyl)boronic esters by reaction with a (dihalomethyl)lithium followed. Attempted displacement of halide from DICHED (2-azido-1-haloethyl)boronates with alkoxides failed. Reaction of either pinanediol or DICHED (2-azido-1-chloromethyl)boronate with sodium acetate in acetic acid yielded the 1-acetoxy derivative as a ∼1:1 mixture of diastereomers, indicating probable involvement of an α-boryl carbocation intermediate. Hydrogenation of the pinanediol azido boronic ester over platinum in a solution of hydrogen chloride in dioxane was accompanied by deacetylation to form the impure (2-amino-1-hydroxyethyl)boronic ester hydrochloride. Attempted purification of this material resulted in deboronation to ethanolamine. Acetylation yielded pinanediol (2-acetamido-1-acetoxyethyl)boronate.     

Zr-Mediated hydroboration: stereoselective synthesis of vinyl boronic esters

An improved process for the preparation of (E)-vinylboronic esters via a Zr-mediated hydroboration of alkynes, especially oxygen-containing alkynes, is described.     

超声条件下制备单取代硼酸

本文报道以硼酸三丁酯为原料与卤代烃，金属镁粉在室温下经超声辐射制备单取代硼酸的结果。该方法操作简单，反应速度快，并得到满意的产率，有一定的应用价值。     

Facile preparation of Hexahydropyrrolo

Chlorolactames 2a-f reacted with sodium azide to give the cyclopropylketimines 3a-f (75-89%), and acid hydrolysis of 3c,d yielded the cyclopropylketones 6c,d (61-67%). Compounds 3a-f and 6c, d were transformed by heating (170-240 degrees C, sublimation) to the air-sensitive dihydropyrroles 4a-f (51-71%) and dihydrofurans 7c, d (85-91%). Oxidation of the dihydro derivatives 4a-f and 7c,d with DDQ led to novel types of pyrrolo[3,2-e][1,4]diazepinedione derivatives 5a-f (75-84%) and furo[1H][3,2-e][1,4]diazepinediones 8c, d (91-93%).     

Facile synthesis of alpha-substituted acrylate esters

Treatment of 5-monosubstituted Meldrum's acids with dimethylmethyleneimmonium iodide (Eschenmoser's iodide salt) in methanol gives alpha-substituted acrylate methyl esters in good yields. Easy access to 5-monosubstituted Meldrum's acids allowed us to synthesize a wide variety of alpha-substituted acrylate methyl esters. The reaction conditions are mild and tolerate many functional groups commonly used in organic synthesis; thus, this new method has potential as an alternative to conventional preparative methods for alpha-substituted acrylate esters.     

Facile transformation of esters to nitriles

Various esters were efficiently converted into the corresponding nitriles in good yields by the treatment with sodium diisobutyl-tert-butoxyaluminium hydride (SDBBA-H), followed by treatment with molecular iodine in aq ammonia. The present one-pot method is very efficient and practical for the conversion of various aromatic and aliphatic esters into the corresponding nitriles.     

Fullerenyl boronic esters: ferric perchlorate-mediated synthesis and functionalization

Fullerenyl boronic esters have been prepared by a ferric perchlorate-promoted reaction of [60]fullerene with various arylboronic acids. The obtained fullerenyl boronic esters could undergo further functionalization with diols to afford C(60)-fused dioxane/dioxepane derivatives. A possible reaction mechanism for the formation of fullerenyl boronic esters has been proposed.     

Asymmetric homologation of boronic esters bearing azido and silyloxy substituents

In the asymmetric homologation of boronic esters with a (dihalomethyl)lithium, substituents that can bind metal cations tend to interfere. Accordingly, we undertook the introduction of weakly basic oxygen and nitrogen substituents into boronic esters in order to maximize the efficiency of multistep syntheses utilizing this chemistry. Silyloxy boronic esters cannot be made efficiently by direct substitution, but a (hydroxymethyl)boronic ester has been silylated in the usual manner. Conversion of alpha-halo boronic esters to alpha-azido boronic esters has been carried out with sodium azide and a tetrabutylammonium salt as phase-transfer catalyst in a two-phase system with water and either nitromethane or ethyl acetate. These are safer solvents than the previously used dichloromethane, which can form an explosive byproduct with azide ion. Boronic esters containing silyloxy or alkoxy and azido substituents have been shown to react efficiently with (dihalomethyl)lithiums, resulting in efficient asymmetric insertion of the halomethyl group into the carbon-boron bond.