Organolithium reagents indicator

The equatorial selectivity observed with organolithium reagents is enhanced in diethyl ether as the reaction solvent by the addition of lithium perchlorate (Table l)12. I3C-NMR studies47 indicate that the formation of a complex between lithium perchlorate and the carbonyl group, which also leads to a dramatic enhancement of the rate of the addition reaction, accounts for the increased diastereoselectivity. 

As indicated in Scheme 1 the outcome of the hthiation of trisamidothiophos-phates SP[N(H)R]3 with organolithium reagents is influenced by the steric bulk... 

The addition compounds (I) are insoluble in diethyl ether, and the slurries obtained are quite stable. In more strongly solvating media, such as tetrahydrofuran or dimethoxyethane, the compounds are soluble but show rapid decomposition, with trimethylamine and polymethylene as the main products. These experiments indicate (9, 40) that when the lithium salt is trapped by donor solvent molecules, the free ylide quickly undergoes decomposition (40). No free trialkylammonium ylide has yet been prepared, even under very mild conditions (35). On the other hand, it has been shown, that the tetramethylammonium cation can even be metalated twice by organolithium reagents (102) to afford dimethyl-ammonium bismethylides ... 

The reaction of cerium reagents with imines and nitriles which possess a-hydrogens has been studied by Wada et al ° Available data indicate that the reagents do not effectively d to these substrates, although the results are better than with alkyllithiums themselves. A modification of the procedure improves the yields of addition products. Thus, addition of the organocerium or organolithium reagent to an... 

Diphenylacetone tosylhydrazone can be used as an indicator in the assay of organolithium reagents (equation 59). Here, the end point, the formation of the orange dianion, is sharp and easily observed. 

Wakefield and Cook have indicated that the high yield and relative absence of side-products by using organolithium reagents make this reaction advantageous in comparison to trimerization of benzonitrile in the presence of organolithium reagents (Section VIII,A,1). 

All the above reactions involve hydrogen—lithium interconversion (metalation). There are a limited amount of data available indicating that N-chelated organolithium intermediates also undergo nucleophilic addition to carbon-carbon double and triple bonds much more readily than does the organolithium reagent alone. Indeed, this enhanced reactivity toward addition reactions is a key factor in the telomerization of ethylene onto aromatic hydrocarbons (6, 7,8,9). 

Butyllithium was purchased from Aldrich Chemical Company, Inc., and titrated with N-benzylidenebenzylamine as indicator according to an established procedure.3 The use of the highly concentrated organolithium reagent is essential because the use of more dilute solutions of butyllithium in hexanes results in precipitation of the lithium acetylide and theretore less efficient coupling with tert-butyldimethylsilyl chloride. 

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