Trimethylsilyl- and a-Alkoxy-Vinyllithium Compounds

In a more recent study Knorr and von Roman 114) investigated the configurational stability of the synthetically interesting 115) a-trimethylsilyl- and a-alkoxy-vinyllithium species 167 and 168. 

1 -Trimethylsilyl-vinyllithium 167a in THF has a half-life for the Z/E rearrangement of 0.11 sat 48 °C. Extrapolation (AH = 7.4 ( 1.5 kcal/mol) and AS = —32( 4) e.u.) to —70 °C leads to a half-life of 0.5-15 min. This is in agreement with qualitative observations in THF 1-silyl-vinyllithium species are configurationally stable only at —70 °C. The same holds for diethylether solutions. In alkane solutions in the presence of TMEDA, on the other hand, configurational lability is only observed at 25 °C. 

The importance of kinetic studies of this sort for synthetic investigations is self-evident. 

6 The Reversible Rearrangement of Acyl-Substituted [9]AnnuIene Anions into Nonafulvenolates as a Function of the Ion Pair Character 

In previous chapters the influence of the gegenion and the solvent on rearrangements of carbanions mostly concerned the rate of a certain reaction (and thus kinetic aspects), as, e.g., in the case of the cyclopropyl-allyl anion rearrangement (Sect. 2.1), the ally anion isomerization (Sect. 2.2), the cyclization of 5-hexenyl alkali metal compounds (Sect. 4) or the configurational isomerization of a-substituted vinyl-lithium compounds (Sect. 5). 

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