Borane oxidation

Borane, trihexyl-, 53, 77 Boranes, oxidation with H2O2,... 

Boranes oxidize in air to form boron oxides. Diborane spontaneously ignites in air around 50°C. The presence of impurities can lower the ignition temperature. Tetraborane decomposes slowly at ordinary temperatures but rapidly on heating. Decaborane is very stable at ordinary temperatures. When heated at 300°C, it slowly decomposes to boron and hydrogen. All boranes decompose to their elements at elevated temperatures. 

These bulkier boranes enhance the regio selectivity of hydrobora tion of trisubstituted alkenes in particular and may also lead to high diastereoselectivity when there is a stereogenic centre next to the alkene. In this next examplej an allylic alcohol is hydroborated with thexyl borane. Oxidation reveals complete regioselectivity and a 9 1 stereoselectivity in favour of hydroboration on the same side as the OH group. 

Borane, bis(3-methyl-2-butyl)-, 53, 79 Botane, trihexyl-, 53,77 Boranes, oxidation with H, O, 50,90 52,59... 

Determination of the optical purity of compounds by HPLC systems equipped with chiral stationary phases has become an indispensable method in enan-tioselective synthesis and P-stereogenic compounds are not an exception. The optical purity of those compounds was traditionally determined by optical rotation or by NMR integration of diastereomeric adducts with several chiral shift reagents, but nowadays the most common way is to analyse the phosphine borane, oxide or sulfide by chiral HPLC. Given the high sensitivity of phosphines to oxygen, analyses are carried out in protected derivatives. In theory, the same methods could be used for the separation of racemates in gram... 

The BV-type transition state involves concerted methyl migration and IO3 loss as observed by stretching of the C-Re bond from 2.168 A to 2.516 A and the I-O bond from 1.803 A to 2.399 A. Similar to BV or alkyl borane oxidation reactions in organic chemistry, this transition state can be described as a formal insertion of an electrophilic O into the Re-CH3 bond. While it is possible that a more exhaustive investigation could lead to alternative low-energy pathways, these results emphasize that a BV-type pathway can be considered as a particularly facile route for M-R functionalizations. 

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