Diastereo‐ and Enantiomerically Pure Allylboronates: Their Synthesis and Scope

Allylboronates are highly attractive reagents for allyl additions. Enantiomerically pure, stable reagents with a stereogenic centre in α‐position to boron are especially versatile, albeit often difficult to synthesize. Starting from boron‐containing allyl alcohols 6 and 7 , which are discussed in detail herein, a set of reagents were obtained via [3,3]‐sigmatropic rearrangements and consecutive transformations in the side chain. The configurations could be established first by chemical correlation, but also by X‐ray crystallography ( 16 , 18 , 34 , and 39 ). Allyl additions were performed resulting in the formation of predominantly ( Z )‐configured homoallylic alcohols ( 31 , 43 – 45 ) with high enantiomeric excess. Detailed investigations on the matched–mismatched interaction between the reagents 15 / 16 (and ent ‐ 15 / ent ‐ 16 , respectively) and isopropylidene glyceraldehyde 42 d are presented.