Crotyl bromide reaction with benzaldehyde

Homoallylic alcohols (8, 111-112). The high rltreo-selectivity observed in the reaction of benzaldehyde with crotyl bromide (either irons or cis) is general for relatively unhindered aldehydes (equation I). High threo selectivity is still observed in the reaction with an a-methyl substituted aldehyde, but a-asymmetric induction (at C3) is rather low (2.2 1) with simple aldehydes (equation II).1... 

The reaction of benzaldehyde with unsymmetrical allylic bromides in the ionic liquid bmim also proceeds regioselectively to realize a carbon-carbon bond formation at the more substituted allylic carbon (Scheme 5). In the coupling of crotyl bromide with benzaldehyde, the product is a nearly 50 50 mixture of antilsyn diastereomers. Cinnamyl bromide predominantly gives the //-diastereomer. The regio- and diastereoselectivity is similar to that observed for these in aqueous media.104... 

The indium-mediated aqueous Barbier-type reaction of crotyl bromide with benzaldehyde shows no diastereo-selectivity. However, the use of preformed crotylindium sesquibromide in DMF affords. sy/z-l-phenyl-2-methyl-3-buten-l-ol (ca. 40% de) after aqueous acidic workup. At 22 °G in DMF prior to workup, a greater relative proportion of //-intermediate is decomposed as compared to its yy/z-diastereomer. The resultant kinetic diastereoselection upgrades the syn anti ratio to 99 1 with a concomitant drop in overall yield (Scheme 14).127... 

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