Addition of Allylboranes to Carbonyl Compounds

A particularly useful borane is the chiral reagent (-)-B-allyl(diisopinocampheyl)borane.l 3 Although the chemistry of acyl addition to aldehydes and ketones to give alcohols will not be formally discussed until Section 8.4.C, the addition of this chiral allylborane to carbonyl compounds will be presented here. In a simple example taken from Smith s synthesis of (-)-macrolactin A,n 156 was treated with (-)-B- 

The reaction proceeds with excellent enantioselectivity as shown, but in some cases the diastereoselectivity is modest, which is true when the allylborane reagent is substituted, as in crotylborane derivatives. In the Omura, Smith and co-workers synthesis of (+)-lactacystin, for example, reaction of the B-crotyl derivative shown with aldehyde 158 gave a 4 1 mixture of 159 and 160 in high yield. Each diastereomer was formed with high enantioselectivity. 

The reader is also directed to Section 12.7.C for a palladium-catalyzed coupling reaction involving boronic acids called Suzuki coupling. 

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