Hydroboration, alkenes Hydrocarbon

Transfers of hydride from boron or lithium to carbon usually occur in the context of addition of the complete M—H moiety to polar or non-polar unsaturation. Additions of boranes to alkenes have been extensively reviewed (Brown et al., 1983a), but the experimental characterization of the hydroboration transition state remains problematic. Dialkylboranes, including 9-borabicyclo[3.3.1]nonane (Wang and Brown, 1980), borinane (Brown et al., 1984), and disiamylborane (Chandrasekharan and Brown, 1985) have now been shown to be dimeric in hydrocarbon and ethereal solvents. With unreactive alkenes, their additions are first order in alkene and half order in the dimer. With reactive terminal alkenes, the reactions are first order only in dimer, with intermediate behaviour between these extremes. A reaction scheme (10) involving reaction of monomeric borane with the alkene satisfies the data, with the observed order depending on the ratio k i/k2. 

The catalytic reduction of alkenes and alkynes are important methods for the synthesis of alkanes. The hydroboration and hydrosilylation of alkenes are alternatives to catalytic methods. Again, both the alkene and alkyne may have played an important role in the construction of the hydrocarbon chain. 

Hunsdiecker reaction, 341 Hybridization, 17 Hybrid orbital number, 17, 18, 32 Hybrid, resonance, 24 Hydration of cyclohexane derivatives, 191 Hydrazine, 4 Hydride shift, 93 Hydroboration, 95 Hydroboration-oxidation, 258, 270 Hydrocarbons, cyclic, 162 unsaturated, 87 Hydrogenation of alkenes, 57 Hydrogen bond, 22 Hydroperoxides in ethers, 284 Hydroquinone, 430 Hydroxy acids, 344... 

Hydroboration, the addition of borane (or diborane) to n-donor substrates such as alkenes, acetylenes, carbonyl compounds, and so on, is a most useful synthetic reaction and was developed by the extensive work of Brown et al. 2 "52 In the absence of more nucleophiUc n- and n-donor sites, borane will also attack a bonds in alkanes, silanes, and aromatic compounds to yield addition, cleavage, and rearrangement products. The interaction of borane with hydrocarbons involves 3c-2e bonded pentacoordinate carbons. 

Hydroboration of the byproduct alkene gives isomeric B-alkyl-9-BBN products. Generally, hydrocarbon solvents are preferable to ether or THF for this process because the greater stability of the intermediate methoxyborate complexes (i.e. Li[R(MeO)-9-BBN]) at —78°C in these solvents prevents the product from being formed and competing with B-MeO-9-BBN for the alkyl-lithium reagent prior to its complete consumption. The complex is stable for alkenyl and alkynyl derivatives which require... 

Purpose. The oxidation of an alkene to an alcohol is investigated via the in situ formation of the corresponding trialkylborane, followed by the oxidation of the carbon-boron bond with hydrogen peroxide. The conditions required for hydroboration (a reduction) of unsaturated hydrocarbons are explored. Alkylboranes are particularly useful synthetic intermediates for the preparation of alcohols. The example used in this experiment is the conversion of 1-octene to 1-octanol in which an anti-Markovrukov addition to the double bond is required to yield the intermediate, trioctylborane. Since it is this alkyl borane that subsequently undergoes oxidation to the alcohol, hydroboration offers a synthetic pathway for introducing substituents at centers of unsaturation that are not normally available to the anti-Markovnikov addition reactions that are based on radical intermediates. 

The problem specifies that a hydrocarbon be the starting material, so hydroboration-oxidation of an alkene is a reasonable possibility for completing the retrosynthesis. 

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