Allylcerium reagents

Cohen et al. have extensively studied the generation and reactivities of allylcerium leagents. - Allylcerium reagents react with a,p-unsaturated carbonyl compounds in a 1,2-selective fashion. It is particularly noteworthy that unsymmetrical allylcerium reagents react with aldehydes or enals mainly at the least-substituted terminus, as opposed to other allylorganometallics such as allyltitanium reagents. An example is shown in Scheme 13. ... 

Another prominent feature is that the reaction at -78 C ffovides (Z)-alkenes, while at -40 C ( )-alk-enes ate formed. Allylcerium reagents have been successMly employed in an economical synthesis of... 

Allylmetallic reagents The ally] anions obtained by reductive metallation of ally I phenyl sulfides with lithium l-(dimethy amino)naphthalenide (LDMAN, 10, 244) react with a, 3-enals to give mixtures of 1,2-adducts. The regioselectivity can be controlled by the metal counterion. Thus the allyllithium or the allyltitanium compound obtained from either 1 or 2 reacts with crotonaldehyde at the secondary terminus of the allylic system to give mainly the adduct 3. In contrast the allylcerium compound reacts at the primary terminus to form 4 as the major adduct. 

Addition to the N=X bonds. Amine synthesis, particularly from chiral hydra-zones, using RCeCL as nucleophiles is well established. " The reagent formed from 1 1 RLi and CeClj is superior to RLi alone or RMgX. For conjugated aldimines, enantioselective 1,2-addition predominates. Allylcerium halide reagents can be pre-... 

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