Potassium trialkylborohydrides

Moderate yields of acids and ketones can be obtained by paHadium-cataly2ed carbonylation of boronic acids and by carbonylation cross-coupling reactions (272,320,321). In an alternative procedure for the carbonylation reaction, potassium trialkylborohydride ia the presence of a catalytic amount of the free borane is utilized (322). FiaaHy, various tertiary alcohols including hindered and polycycHc stmctures become readily available by oxidation of the organoborane iatermediate produced after migration of three alkyl groups (312,313,323). 

Uses. Brown has published details of his recent work on potassium hydride. It is particularly useful for preparation of hindered bases such as potassium bis-(trimethylsilyl)amide. It is useful for preparation of potassium enolates from ketones, without reduction or aldol condensation. Metalation of 2-methyl-cyclohexanone with KH gives an equilibrium mixture of potassium enolates. However, the less substituted enolate can be obtained as the product of kinetic control by use of potassium bis(trimethylsilyl)amide. Another important use of KH is for preparation of hindered potassium trialkylborohydrides, which are valuable for reduction of ketones to the less stable alcohols. 

The reaction of potassium hydride in THF with trialkylboranes has been found to proceed smoothly at 25 °C to produce the corresponding potassium trialkylborohydrides. A very complete study concerning steric effects in the reaction of a series of trialkylboranes with lithium and sodium hydrides in THF has been carried out. Sodium hydride exhibited greater reactivity than lithium hydride and the reactivity of the organoboranes decreased drastically as the steric hindrance increased. ... 

Alkali metal trialkylborohydrides are attractive reducing agents in addition to other numerous synthetic applications [1], Brown and coworkers [2] have also synthesized alkali metal di- and monoalkylborohydrides. Consequently, the reaction of lithium, sodium, and potassium hydrides with 9-BBN, ChXjBH, Sia BH, IPCjBH, ThxBHj, and IPCBHj afford the corresponding hydrides, which are examined with respect to rate, stoichiometry, and products. 

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