The Reaction of Trialkylboranes with Methyl Vinyl Ketone and Acrolein

Trialky I boranes react rapidly with methyl vinyl ketone (and other a,j8-unsaturated ketones) to yield, after hydrolysis, methyl ketones of the indicated structure 4). The reaction with acrolein is analogous to give jS-alkylpropionaldehydes (5). The process is inefficient in that only one of the three alkyl groups of the borane is converted into product, but the rapidity and ease of carrying out the reaction may be adequate 

Trioctylborane with Methyl Vinyl Ketone 2-Dodecanone 4) 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

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