Search

The first synthesis of (plusmn)-C-aryl-6-fluoro and -6,6-difluoro olivosides is described through the allylic mono- and difluorides produced by regioselective fluorination of hydroxyalkyl and oxoalkyl derivatives respectively. A preliminary study points out the efficiency of the straightforward sequence in C-alkyl series.

Research shows that sulfide-borane complexation increases from thioanisole to dimethyl sulfide with ether, sulfides, and dialkyl sulfides in between and in that order. However, the reactivity of the borane adducts toward 1-octene increases in the reversed order. Data suggest that the dialkyl sulfides are useful as borane and chloroborane carriers.

A study showing that N,N-dialkyl-tert-alkylamines are convenient borane carriers for hydroboration is demonstrated. The alkylboranes obtained after hydroboration were oxidized with hydrogen perodixe/sodium hydroxide and the product alcohols were obtained in quantitative yields.

The description of the method for the stereocontrolled cyclopropane synthesis is presented. Experiments include direct hydroboration of alkynes by means of the chiral 1,3,2-dioxaborolane.

An investigation into the regiochemistry of addition to the fulleroid C61H2 by Zn(Cu) reduction and hydroboration was conducted. One major isomer is formed by hydroboration while two major isomers of C61H4 were formed by the reduction with Zn(Cu). The structures of the major isomers formed by reduction with Zn(Cu) were identified as 1,2-C6H4 and 3,4-C61H4. The regiochemistry observed in the formation of 1,2-C61H4 was the same regiochemistry seen in the further reactivity of azafulleroids.

Trans-fused bicyclic and cyclic ketones and secondary alcohols in high optical purities were synthesized through asymmetric cyclic hydroboration of suitable cyclic dienes with enantiomerically pure isopinocampheylchloroborane etherate. Asymmetric cyclic hydroboration was found to be a highly efficient, simple and convenient procedure for synthesizing various trans-fused polycyclic and cyclic ketones. Highly stereo- and enantioselective annelation was achieved for the synthesis of the ketones and secondary alcohols.

Computational studies were performed to examine three pathways leading from B4H10 + C2H4 to the basket compound (CH2CH2)B4H8. Results showed that the preferred mechanism involves H2 dissociation from B4H10 as the rate determining step and the consecutive formation of two intermediates. While the second pathway involving ethene hydroboration was excluded because of the too high energy required, path I consisting of a B4H10 isomer as a hydroborating agent was considered competitive and selected as the most favorable path.

The H3B-NPhEtPr amine-borane adduct was used in hydroboration studies of representative olefins, such as 2,3-dimethyl-2-butene, alpha-pinene, 2-methyl-2-butene, cyclohexene, norbornene, cyclopentene, beta-pinene, styrene and 1-hexene, in dichloromethane, n-pentane, methyl ether, tert-butyl, dioxane and tetrahydrofuran at room temperature. For dioxane, the reactions were more expedient, requiring only 0.5 up to one hour for hydroboration. On the other hand, hindered alpha-pinene and 2,3-dimethyl-2-butene structures rapidly produced stable monoalkylboranes.

A single-crystal X-ray diffraction analysis of the structure of the organodiborane (mu-H)2(BC5H10)2 was conducted. The study also addressed its reactions with nucleophiles and its conversion to the cyclic organohydroborate anion, [H2BC5H10]-. The findings indicate that the anion functions as a facily hydride transfer agent in its reduction of NH3THF and 4-tert-butylcyclohaxanone. The anion also acts as a chelating ligand to form cyclic organohydroborate complexes.

A study was conducted on two regioselective, high-yield routes to nido-6-alkyldecaborane(14)s via one-pot syntheses. The findings indicate an addition reaction between alkyllithium reagents and salts of nido-B10H13- to form arachno-6-R-B10H13 (super 2-). Moreover, olefin hydroboration of arachno-6,9-(SMe2)2-B10H12 results in nido-6-R-8-(SMe2)-B10H11 which may be reduced to nido-6-R-B10H12-.

The formation of a new borylidyne cluster from the reaction of (mu-H)2Os3(CO)10 and BH3S(CH3)2 was described. Nuclear magnetic resonance spectroscopy results were similar to the spectra results of iron and ruthenium borylidyne clusters. Bond angles and distances between the osmium and carbon showed the presence of bridging hydrogen atoms. The two types of structures described reflect the role of the transition metal in the position of the bridging hydrogens.

The hydroboration reactions of six sterically different 2-organylapopinenes with 9-borabicyclo(3.3.1)nonane in a 1:1 molar ratio in tetrahydrofuran have been examined. The results showed that the rate of hydroboration decreases as the R group in the 2-R-apopinenes became bulkier. The synthesis of optically pure B-(2-organylapoisopinocampheyl)-9-borabicyclo(3.3.1)nonanes is also presented.

The synthesis of optically pure isopinocampheylchloroborane, (IpcBHCl) reagent is carried out by numerous simple methods with the formation of IpcBH2 and IpcBCl2 as side products. The hydroboration reaction of prochiral alkenes involves its reduction-hydroboration reaction with IpcBCl2 and LAH in ethyl ether at -25 degrees celsius. The synthesis of chiral 2-organylapoisopinylhaloboranes for asymmetric synthesis through chiral organoboranes is an application of this method.

Dicarbonyltitanocene (Cp2Ti(CO)2) and dimethyltitanocene (Cp2TiMe2) were used as catalysts in the hydroboration of alkynes and alkenes, respectively. Cp2Ti(CO)2-catalyzed hydroboration of alkynes resulted in the complete conversion of the alkyne, the single addition of borane and the formation of anti-Markovnikov products with terminal acetylenes. Hydroboration of alkenes with Cp2TiMe2 required ligand substitution with an alkene and resulted in the formation of anti-Markovnikov products with high selectivity. These results indicated that Cp2Ti(CO)2 and Cp2TiMe2 are effective and highly selective catalysts for hydroborations of alkynes and alkenes.

The reactions of organoruthenium phosphine complexes with hydroborating reagents involve the B-C bond formation. The easy Ru-H/Ru-H-B exchange and Ru-H-B interactions occur due to Lewis acidity of the resulting three-coordinate boron. The reaction mechanism involve the loss of PMe3 from the electron-rich ethylene and benzyne complexes, reaction of the phosphine-borane with a second equivalent of borane through B-C bond formation and C-H bond activation to form ruthenium hydrides.

Beta-amino alcohols can be obtained in very good yield by hydroboration of acyclic and cyclic aldehyde and ketone enamines with mono- and dialkylboranes followed by their oxidative reduction. The trialkylboranes obtained from enamines using 9-borabicyclo(3.3.1)nonane(9-BBN) underwent an methanol-promoted elimination reaction to associated alkenes.

Use of the ab initio molecular orbital method helps investigate the hydroboration of olefins. This rhodium(I)-catalyzed reaction proceeds through the formation of an intermediate by insertion of C double bond C into the Rh-B bond. Isomerization of this intermediate, followed by reduction and coupling with regeneration of the catalyst, complete the reaction. This is the most preferred mechanism, the slowest step of which is elimination by reduction.

Reactions of catecholborane (HB(cat)) with related phosphinorhodium(I) complexes and with several phosphine ligands were examined and implications for transition metal-catalyzed hydroboration of alkenes were reported. Reactions of HB(cat) with phosphines give different boron-substituent redistribution products depending upon steric component of the phosphine. Phosphinorhodium(I) hydrides also gave boron-substituent redistribution products.

The reaction of BH3 THF or BH3 SMe2 with 2,4,4-trimethyl-2-pentene was used to prepare DIBborane in qunatitative yield. Examination with IR and 11B nuclear magnetic resonance revealed that DIBborane was a symmetrically bridged dimer in THF and that it forms the corresponding boronic acid or dimethylboronate ester by reacting with water or methanol, freeing hydrogen. Results also revealed that DIBborane and thexylborane reacted with various bases, S(CH3)2, pyridine, N(CH3)3, TMED and NEt3 to procude addition compounds. DIBborane was found to be a weaker Lewis acid than thexylborane and to be a sterically demanding monoalkylborane.

The addition of boron-hydrogen bond to various carbon-carbon and carbon-heteroatom double bond is studied using the Interactive Generation of Organic Reactions 2 program. The resulting reactions indicate that the hydroboration of enamines can give both alpha and beta-adducts. It is also found that the alpha and beta adducts ciuld undergo rearrangement to produce the corresponding B-aminomonoalkylborane.

The hydroboration of (mu-H)2Os3(CO)10 in CH2Cl2 with a THF/B2H6 ratio greater than 2/1 yielded (mu-H)3Os3(CO)9(mu3-BCO) or (mu-H 3Os3 CO 9 mu3-C-single bond)3(O3B3O3). The structure of the second cluster consists of a hexagonal B3O3 ring with three triosmium methylidyne cluster units coordinated to it. Moreover, the proposed scheme for the cluster's generation involves the conversion of a terminal carbonyl ligand to a triosmium face-capping carbonyl.

Borane-1,4-thioxane readily hydroborated alkenes in different solvents at 25 degrees celsius or with neat reagents at 0 to 25 degrees celsius to form the corresponding partially substituted borane reagents in good yields. Variation of the stoichiometric ratio of the alkenes determined the outcome of the reaction. The hydroborating reagent was prepared from the reaction of diborane with 1,4-thioxane. Reactivity studies further characterized the structure and reaction behavior of borane-1,4-thioxane.

Various olefins underwent hydroboration with the addition of catecholborane in the presence of rhodium(I) and iridium(I) catalysts. Mechanistic studies revealed that the net transformations of uncatalyzed and catalyzed hydroboration were similar. However, both processes featured significantly different reaction mechanisms in forming common products. Moreover, the catalyzed hydroboration of allylic alcohols provided isomers that complemented those of uncatalyzed hydroboration conditions.

Rhodium(I)-catalyzed hydroboration involved a multistep mechanism resembling that of transition metal catalyzed hydrogenation of olefins. Both processes proceeded through the migration of a hydride to the bound olefin. The application of isomerization and deutrium labeling studies identified the observed substrate-dependent level of reversibility and fundamental hydroboration catalytic cycle.

Beta-alkyldiisopinocampheylboranes' (Ipc2BR) reaction with aldehydes leads to a nonenzymatic asymmetric synthesis of chiral boronate esters with an enantiomeric excess of not more than 99% from the former 81% to 96%. Aldehydes that have electron-deficient carbonyl groups have a faster rate of reaction. For this reason, addition of a Lewis acid increases the electron deficiency of aldehydes and hastens the reaction rate. The addition of aldehydes eventually results in the kinetic resolution of intermediate boronic esters.

The alpha-alkoxy group provides effective regio- and stereocontrol in the hydroboration of methyl beta,gamma-enoates with borane-methyl sulfide. The study shows that the alpha-OMe oxygen induces hydride reduction of the ester, creating a dialkoxy borane intermediate. Upon alkaline oxidation (H202/NaOH), the intermediate undergoes intramolecular dihydroxylation that results in a 1,3-diol. The reagent favors the formation of2,3-anti diastereomers. Both regio- and diastereoselectivities disappear when the alpha-OMe is replaced by a methyl group or when the ester is not activated.

The development of a mild and general method for the synthesis of cis-alkenyl pinacolboronates and potassium organotrifluoroborates with corresponding terminal alkynes as starting material is reported. The alkynyl pinacolboronates bearing various functional groups are stereoseletively reduced to the cis-alkenyl pinacolboronates via hydroboration with dicyclohexylborane.

Two stereocomplementary approaches are used for erythro/trans and threo/cis vicinal amino diol subunits containing 2-pyrrolidinones. A formal asymmetric synthesis of (-)-detoxinine is achieved by using hydroboration-oxidation reactions.

The new tripod ligands bis(pyrazolyl)(3-tert-butyl-2-thioimidazol-1-yl)hydroborate (L(super 1)) and bis(pyrazolyl)(3-isopropyl-2-thioimidazol-1-yl)hydroborate (L(super 2)), together with zinc nitrate or zinc chloride and the corresponding thiolates, have yielded a total of 17 zinc-thiolate complexes. Hydroborate ligands L(super 1) and L(super 2) have enabled a further step in systematic investigation on the modeling of biological thiolate alkylations by zinc enzymes.

High yields of hydroboration products in the absence of a metal catalyst are observed when decaborane olefin-hydroboration reactions are executed in ionic liquids (IL). The results indicate that dicaborane reactions with alkynes in ILs result in alkyne-infusion providing a new route to o-carboranes.

Research was conducted to examine a smooth thermal rearrangement that can be performed with acyclic tetrasubstituted olefins. Results demonstrate that the thermic rearrangement of tertiary organoboranes readily obtained by the hydroboration of tetrasubstituted olefins produces a variety of primary organoboranes corresponding formally to an allylic functionalization of the starting olefin. The high stereoselectivity of the migration makes the reaction very useful for the stereoselective synthesis of open-chain products.

Research was conducted to examine the diastereoselective hydroboration of isopropenylcyclopropanes. The alcohol was derived as a single diastereoisomer in good isolated yields when cyclopropane was hydroborated using either 9-BBN-H or BH3*THF in THF followed by a standard format. Other substituted isopropenylcyclopropylcarbinols were also investigated to expand the scope of the reaction. Results indicate that the hydroboration of cis-isopropenylcyclopropanes proceeds with a high degree of stereocontrol.

A study was conducted where a titanium-catalyzed reaction was discovered that allowed the systematic, high-yield syntheses of monoalkyldecaboranes. The catalyst was also active for long periods. It was also found that the titanium-catalyzed reactions of decaborane with non-conjugated diolefins such as 1,5-hexadiene give high yields of either alkenyl-substituted (88%) or linked-cage products (92%) depending upon reaction conditions and stoichiometries.

A study was conducted on a facile synthesis of novel well-defined pi-conjugated systems by polyaddition using the well-known hydroboration reaction. The findings indicate that the extension of the pi-conjugation length via the boron atom can be observed in the organoboron main-chain polymers prepared by hydroboration polymerization. Moreover, blue fluorescence emission was also observed.

The propensity of ligands toward transient ring slippage and the consequent coordinative unsaturation is a viable approach to directed reactions. An examination of the chemistry of (eta(super 5)-Ind)Rh showed that the alkyl ether directed the hydroboration of 4-(benzyloxy)cyclohexene and that the eta(super 5) to eta(super 3) ring slippage afforded the necessary level of coordinative unsaturation at the metal. It is the first known report of an alkyl ether-directed, metal-catalyzed olefin hydroboration.

Research was conducted to examine the synthesis, hydroboration, and reduction of new, highly reactive tert-butyldialkylamine-borane adducts. The adducts with N,N-dialkylaninilines, alkyldiisopropylamines and N-silylamines were successful in hydroborating 1-octene in tetrahydrofuran at room temperature in less than an hour. Therefore, aliphatic amines have been shown to be useful borane carriers for hydroboration. It was also revealed that borane complexation depends strongly on the steric requirements of the amine.

The hydroboration reaction demonstrates regiochemical and stereochemical control. An experiment involving the hydroboration of 1-tert-butylcyclohexene illustrates both of these outcomes through a Jones oxidation test and a melting point. The mechanistic aspects of the hydroboration reaction are illustrated in this simple reaction. The Jones test is negative with 1-tert-butylcyclohexanol but positive with 2-tert-butylcyclohexanols.

A new technique for hydroboration of olefins provides a simple way to produce chiral alkyl boranes with essentially 100 percent optical purity. The technique, developed by nobel laureate Herbert C. [...]