Addition Hydroboration, Markownikoff

The overall result of the sequence hydroboration -I- oxidation is a regioselective and-Markownikoff-addition of water to an alkene. This reaction is an important method in organic synthesis, since it can be made stereoselective and even enantioselective. 

The hydroboration of olefins at about room temperature leads to trialkylboranes by anti-Markownikoff addition 20) ... 

Isopinocampheol has been prepared by hydrogenation of nickel catalyst at 70-100°. The hydroboration reaction provides a convenient procedure for the conversion of olefins to alcohols without rearrangement and with a predictable stereochemistry. The reaction has been applied to a large number of olefins of widely different structures.4,6 The results obtained support the proposed generalization that hydroboration involves an awfi-Markownikoff, cia-addition of borane from the less hindered side of the double bond. ... 

Thus hydroboration of a double bond followed by peroxide oxidation is a convenient procedure for converting the olefin into the alcohol corresponding to anti-Markownikoff addition of water. 

The hydroboration of an olefin involves a cis addition of a boron-hydrogen bond to an alkene linkage, and for unsymmetric olefins occurs in a counter-Markownikoff fashion. 1-Alkenes and simple 1,2-disubstituted olefins undergo rapid conversion to the corresponding trialkylborane, whereas addition of diborane to tri- and tetrasubstituted olefins may be conveniently terminated at the respective di- and monoalkylborane stage. 1-Alkenes yield trialkylboranes in which there is a preponderant (approximately 94%) addition of the boron atom to the terminal carbon.2,3... 

Hydroboration. When these two reagents are mixed in THF, hydrogen is evolved and a solution of a violet titanium-boron complex forms. This complex catalyzes the hydroboration of alkenes with LiBH4 to form lithium alkylboro-hydrides, which are converted to alcohols by NaOCHj and H2O2. The relative reactivity of alkenes is terminal > cyclic > internal. The reaction involves anti-Markownikoff addition. 

The direction of addition of the B-H bond to atrisubstituted double bond seems to be determined by the addition of the more electronegative hydrogen atom to the more highly substituted carbon atom of the double bond. Thus, with the B H bond assumed to be polarised in the sense B " —the process may be considered in terms of the electronic arguments summarised in the modern interpretation of Markownikoff s rule for ionic additions to double bonds [15]. The outcome of the hydroboration/oxidation sequence corresponds to an "anti-Markownikoff hydration of the double bond, which has many synthetic applications. If steric factors are also important, these of course operate in the same sense, generally favouring attachment of boron to the less-hindered secondary carbon atom. 

Hydroboration-oxidation gives anti-Markownikoff addition of water across the carbon-carbon double bond. 

A mixture of bicyclo[2.2.1]heptadiene, glacial acetic acid, and tris(triphenyl-phosphine)platinum(O) heated 64 hrs. at 120° under Ng in an autoclave exo-5-acetoxybicyclo[2.2.1]hept-2-ene. Y 95%. E. F. Magoon and L. H. Slaugh, J. Organometal. Chem. 55, 409 (1973) n//-Markownikoff addition to prim, acoxy compds. by hydroboration-mercuration-iodination cf. R. C. Larock, J. Org. Chem. 39, 834 (1974). 

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