Trialkylboranes with methyl vinyl ketone

Brown proposed a mechanism where the enolate radical resulting from the radical addition reacts with the trialkylborane to give a boron enolate and a new alkyl radical that can propagate the chain (Scheme 24) [61]. The formation of the intermediate boron enolate was confirmed by H NMR spectroscopy [66,67]. The role of water present in the system is to hydrolyze the boron enolate and to prevent its degradation by undesired free-radical processes. This hydrolysis step is essential when alkynones [68] and acrylonitrile [58] are used as radical traps since the resulting allenes or keteneimines respectively, react readily with radical species. Maillard and Walton have shown by nB NMR, ll NMR und IR spectroscopy, that tri-ethylborane does complex methyl vinyl ketone, acrolein and 3-methylbut-3-en-2-one. They proposed that the reaction of triethylborane with these traps involves complexation of the trap by the Lewis acidic borane prior to conjugate addition [69]. 

Reaction with trialkylboranes. A trialkylborane (1), readily available by hydro-boration of an alkene, undergoes fast 1,4-addition to methyl vinyl ketone to give an enol borinate ester (2), which on hydrolysis affords a methyl ketone (3).24... 

Reaction with trialkylboranes. The reaction of trialkylborancs with acrolein (2, 15) and with methyl vinyl ketone (2. 284-185) yields, respectively, aldehydes and methyl ketones. However, the reaction is not directly applicable to all a,/3-unsaturated carbonyl compounds. Thus /ram-crotonaldehyde (I) and mesityl... 

Diketones can be obtained by the Michael-type reaction of trialkyl-alkynylborates with methyl vinyl ketone in the presence of TiCl4 (Scheme 5). The reactions of bis(trimethylstannyl)butadiyne with trialkylboranes also involve alkynylborates. Use of 9-BBN derivatives has advantages for the synthesis of trisubstituted ethenes from lithium alkenyltrialkylborates. Alkenylborates for such reactions can be obtained from the corresponding tosylhydrazones. ... 

The reaction of MVL with trialkylboranes gave vinyl borate salts 536, which suffer alkyl migration at room temperature to give salts 537. These compounds can be transformed into vinyl ethers or methyl ketones by oxidation with hydrogen peroxide (Scheme 144)819. 

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