The reaction of disiamylborane with enol acetates derived
from an aldehyde bearing two α-hydrogen atoms involves a slow anti-Markownikoff hydroboration followed by rapid elimination
and re-hydroboration reactions. Selectivity between reaction of
the cis and trans isomers is far smaller than for the corresponding
olefinic hydrocarbons. Enol acetates derived from ketones are
generally unreactive to disiamylborane.
The extent of reaction of propionic acid with a representative
series of trialkylboranes depends on the steric resistance of the
borane to the initial co-ordination of the acid. The extent of
protonolysis decreases with an increase in the total number of
alkyl substituents at the α- and β-carbon atoms to boron.
With an unsymmetrical trialkylborane the selectivity between the
breaking of secondary and primary carbon-to-boron bonds is
small. A very large selectivity is found in favour of the removal
of a primary—rather than a tertiary—alkyl group. This is thought
to be due to steric and not electronic factors. [Continues.]
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy at Loughborough University.