Alkenyl- and Alkynyl-metal Compounds

Metallation of propargylic compounds, RCHgC CPh (R = H or Me) by excess BuLi provides mono- and di-lithio derivatives, RCHLiC CPh and RCLigC CPh kinetics of the reactions in EtgO at 25 °C were studied.  

An ab initio calculation (RHF/STO-3G level with subsequent RHF/4-31G and RHF/6-31G treatment) on allyl-lithium confirmed the C bridged species (19) as having the lowest energy. The allyl fragment of this structure is significantly distorted from a planar arrangement in order to enhance bonding between the allyl anion HOMO (on C-1 and C-3) and the Li p-orbital with axis parallel to C-1—C-3. 

The WW-shaped dianions (24) are the sole products of reaction of RCH== C==(CH2CH—CHa)2 (25 R = Ph or H) with BuLi in THF. The mono-anion intermediates were shown to be more readily metallated than are the trienes (25). The barriers to rotation of C-1—C-2 and C-4—C-5 in (24 R = Ph) were calcu- 

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