Boranes in Organic Chemistry 1. О±-Carbonylalkyl- and ОІ-Oxyalkylboranes in Organic Synthesis

This review is devoted to the synthesis of a-carbonylalkyl- and ОІ-hydroxy-alkyl boranes and their use in organic synthesis. a-Carbonyl-alkylboranes include several heteroatomic compounds, in particular, [1.2.3]-diazaborinines, uracyl boronic acids, and [1.2.3.4]-diaza-diboretes. The latter type has been obtained by the ketene aminoborations. The reactions of halogenboranes with diazoesters and sulfur ylides resulting in formation of a-carbonyl alkylborates containing diazofunction or ylide structural fragment are described. Amino and halogen boration of acetylenic acid esters was also used for the synthesis of a-carbonyl alkyl boranes. Reactions involving Cr-carbene complexes and acetylenic borone esters were presented for the synthesis of naphthoquinone boronic acids. The formation of amidoboranes by boration of dichloroacetanilides was remined. Boration of 4,8-dimethoxy-2-quinolone with trimethylborates leading to 2-quinolone-3-boronic acid was described. The common synthetic method to a-carbonyl alkyl boranes based on the hydroboration of acrylic acid derivatives was discussed. The results of enhydrazones hydroboration, leading to stable cyclic complexes have been mentioned. The interaction of a-bromoketones with trialkyl or dialkylboranes represents as a general synthetic method to a-carbonyl alkyl boranes. Synthetic approaches to Гў-hydroxy alkyl boranes are performed. The wide spread hydroboration of vinyl and allyl esters received a well-described attention. The hydroboration of cyclanone enol acetates, 3-keto- and 17-keto-steroids and cyclic allyl alcohol acetates was discussed. The results of aliphatic and alicyclic vinyl esters (including dihydrofuran derivatives) boralylation leading to ОІ-hydroxy alkyl boranes have been envisaged. The synthesis of optically active ОІ-hydroxy alkyl boranes using chiral borane hydrides was discussed. The heterocyclic boran dihydrides are obtained by the hydroboration of dihydropyranes, chromenes and flavenes. Borosilylation of allyl allenylic esters was also been envisaged. The synthetic scheme to optically active boranes and further optically active alcohols were presented. The problems of selectivity regularities in hydroboration reaction by intermolecular complex formations have been discussed

Boranes in Organic Chemistry 2. ОІ-Aminoalkyl- and ОІ-Sulfanylalkylboranes in Organic Synthesis

Problems on using of ОІ-aminoalkyl- and ОІ-sulfanylalkylboranes in organic synthesis are considered in this review. The synthesis of boron containing a-aminoacids by Curtius rearrangement draws attention. The use of ОІ-aminoalkylboranes available by enamine hydroboration are described. Examples of enamine desamination with the formation of alkenes, aminoalcohols and their transformations into allylic alcohol are presented. These conversions have been carried out on steroids and nitrogen containing heterocyclic compounds. The dihydroboration of N-vinyl-carbamate and N-vinyl-urea have been described. Examples using nitrogen and oxygen containing boron derivatives for introduction of boron functions were presented. The route to borylhydrazones by hydroboration of enehydrazones was envisaged. The possibility of trialkylamine hydroboration was shown on indole alkaloids and 11-azatricyclo-[6.2.11,802,7]2,4,6,9-undecatetraene examples. The synthesis of ОІ-sulfanyl-alkylboranes by various routes was described. The synthesis of boronic thioaminoacids was carried out by free radical thiilation of dialkyl-vinylboronates. Ethoxyacetylene has been shown smoothly added 1-ethylthioboracyclopentane. Derivatives of 1,4-thiaborinane were readily obtained by divinylboronate hydroboration. Dialkylvinylboronates react with mercaptoethanol with the formation of 1,5,2-oxathioborepane derivatives. Stereochemistry of thiavinyl esters hydroboration leading to stereoisomeric ОІ-sulfanylalkylboranes are discussed. Examples of radical thiilation of various structural types vinylboronates were presented. In particular, 1,3,2-dioxaborinanes and 1,3,2-dioxaborolanes, containing by boron atom vinyl-, propenyl-, isopropenylor isopropylidene substituents have been used. Thiilation has been achieved by use of alkylmercaptanes, as well as mercaptamine derivatives. Alkylmercaptanes were able to replace the bromine substituent in tris-(2-bromoctyl)-borane.  Dialkylvinylborates have been added hydrosulfite with the formation of 2-boronoethane sulfuric acids. A lot of examples of radical thiilation of vinylboronic acid dialkyl esters with mercaptoacids are presented. Under the azaisobutyric acid dinitryle conditions thioglycolic, ОІ-mercaptopropionic, 2-mercaptoamberic acids and their esters as well as cysteine were added. Vinyl-, propenyl- and isopropenyldioxaborolanes were also participated in the thiilation with the formation of acetic, propionic or amberic acid thioethanoboronates. The high reactivity of B,B,B-trivinyl-N,N,N-triphenylborazine in the reaction with thiophenol, leading to B-tris-(phenylmercaptoethyl)-N-phenylborazine was shown. The problems of asymmetric hydroboration leading to chiral ОІ-sulfanylalkylboranes were discussed briefly. In particular, an example, including dihydro-thiophene hydroboration, leading to (+)-R-thiofan-3-yl-diisopinocamphenylborane, and the interaction with acetaldehyde with the formation of (+)-R-3-thiophanyl-diethoxyborane was implemented. The reaction with 3,4-dihydrothiapyrane proceeds analogously. A synthetic route to sulfono-norbornen-boronic acid esters by Diels-Alder reaction of cyclopentadiene with arylsulfanyl-vinylboronic acid esters has been discussed

Boranes in Organic Chemistry 3. О±-, ОІ- and Оі-Haloalkylboranes: The Perspective Vehicles for Organic Synthesis

The methods of synthesis of α− and β−haloalkylboranes, including chloration of alkylboronic acid esters, additive bromation and chloration of esters of vinyl- and alkenylboronic acids, addition of bromine to trivinylborazines have been considered. The reactions of radical addition of polyhaloidmethanes to vinylboranes, α− and β−unsaturated boronic esters, B-vinyl-B-arylboronic esters, B-trivinyl-B-triarylborazines were discussed. The hydroboration of acetylenic halogenides of dicycloalkylboranes, which led to halocontaining derivatives of dialkylvinylborane was separately considered. The examples of hydroboration of halogenides of allyl and vinyl types are presented.The reaction of dienic synthesis, which takes place between vinylchloroboranes or vinylboronic esters and tetra- or hexachlorocyclopentadienes has been discussed. The reaction of alkenes and allenes with boron tribromide was described. The Markovnikov and non- Markovnikov hydrobromation of boron vinylderivatives has been envisaged. The approaches to the synthesis of perfluoroalkylboranes on the base of hydroboration of perfluoroalkenes have been discussed. The methods of the synthesis of boronates, containing halogetaryl substituents, have been performed. The reactions of hydroboration of halogenides of allylic and propargylic types by 9-borabicyclononane have been shown. The regio- and stereoselectivity of the reaction has been discussed. The examples of the synthesis of boranes of the norbornene type were presented. The reaction of boroallylilation of allyl- and propargylhalogenides leading to the derivatives of 3-bora-bicyclo[3,3,1]-nonane has been discussed. Some directions of using of haloidalkylboranes in the synthesis have been discussed. The examples of nucleophilic substitution leading to oxyalkyl- and azidoalkylboranes have been presented. The route of obtaining of alcohols from α−haloidalkylboranes has been shown. The general scheme of synthesis of α−aminoboronic acids was perfomed. The general approach to the synthesis of allenes on the base of hydroboration products of propargyl halogenides has been discussed. The schemes of synthesis of 1,4-disubstituted-1,2,3-butatrienes are presented. The wide using reaction of introducing of vinylic group into substituent, bonding with boron atom in molecules of dialkylvinylboranes, was discussed. The reactions of new C-C bonds formation, based on the action of iodine on the  alkylvinylboronates leading to 1,3-dienes and alkylidencyclanes have been shown. Τhe route of the synthesis of cyclopropanes from β−haloidalkylboranes has been discussed