Crotyllithium

There are relatively few theoretical studies available relating to the dissociation energies of allyllithium species. Theoretical calculations of the CNDO/2 type, which are recognized to give rather inaccurate values of electronic energies, provide a value 74",75) of 201 kcal/mole for the dissociation energy of m-crotyllithium (Eq. (4))... 

Waak 15) also used other unsaturated lithium organic initiators (such as allyl-lithium, crotyllithium) for styrene polymerization. Though more efficient than vinyllithium, these initiators exhibit the same disadvantages. Therefore, the same conclusions apply. 

Crotyllithium was synthesized from tetracrotyltin and butyllithium in pentane and purified by reprecipitation from dimethyl ether with the help of pentane (17). 

Crotyllithium and crotylpotassium compounds can assume either the endo- or exo-configuration. Due to their planarity, both forms are stabilized by electron delocalization. 

While equilibration of the endo- and exo-forms of crotyllithium is very fast, the corresponding potassium reagents are remarkably stable and may be intercepted with electrophiles (E" ).- However, after several hours, the crotylpotassium compounds also equilibrate, surprisingly favoring the endo-form over the sterically less hindered exo-form. ... 

Crotyllithium reagents are ambident nucleophiles and can react with electrophiles either at the a- or y-carbon. The regiochemistry of attack depends on many factors, such as structure, the electrophile, and the solvent. Generally, unhindered carbonyl compounds preferentially add to crotyllithiums at the y-position. 

The reactions of aldehydes with crotylboron ate complexes have also been investigated. Ate complex (56), generated by the addition of Et3B to crotyllithium, exists mainly as the ( )-isomer and displays moderate selectivity (68-85%) for the anti diastereomer in reactions with various aldehydes (Scheme... 

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