Enantioenriched Oxygenated Allylic Stannanes

Enantioenriched Oxygenated Allylic Stannanes 10.10.1 a-Oxygenated Allylic Stannanes... 

A sequence was later developed for the synthesis of enantioenriched a-oxygenated allylic stannanes that did not require resolution (Eq. 33) [53]. This sequence, like the former, starts with the addition of BusSnLi to an enal. The resulting lithio alkoxide is oxidized in situ to the corresponding acylstannane. Reduction of the acylstannane with (M)-BINAL-H affords the (5)-a-hydroxy allylic stannane in > 95% ee. The use of (F)-BINAL-H leads to the (R) enantiomer with comparable ee. These hydroxy... 

The MgBr2-promoted additions are strongly substrate-controlled. As a result it is possible to effect kinetic resolution of racemic y-oxygenated allylic stannanes thereby circumventing the need to employ enantioenriched stannane. The degree of enantio discrimination is somewhat dependent upon the y-oxygen substituent as illustrated by the additions to a threonine-derived aldehyde given in Eq. (46) [66]. 

Lewis-acid promoted cyclizations of allylic stannanes have been successfully employed to prepare macrocyclic compounds. An enantioenriched a-oxygenated allylic stannane led to a 14-membered cembrane precursor in high yield with excellent diastereoselectivity (Eq. 64) [80]. 

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