Allyltin reagents transmetallation

Under thermodynamic control, the homoallylic alcohol is obtained with an anti/syn selectivity up to 95 531-33. In order to prevent competition between the transmetallation and the complexation of the aldehyde, it is important that the allyltin reagent is added first to the Lewis acid. This is termed a reverse addition . 

If the presence of sensitive functional groups poses problems of chemoselectivity in the use of hard allylmetal reagents, allylboronate derivatives can also be accessed by transmetallation of allyltin species with boron halides [29], This approach was used by Corey in the synthesis of chiral bis(sulfonamido)boron reagents (Section 6.3.1.3) [30]. Recently, Williams and co-workers employed this mild approach to synthesize the highly functionalized allylboron reagent 9, which was employed in a key aldehyde allylboration reaction en route to the total synthesis of leucasdandrolide A (Equation 5) [31]. 

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