Potassium reagents

Early work has shown that the reaction of simple organolithium reagents with oxiranes lead mainly to products from a- or -deprotonation and not from the desired ring opening reaction. However, some reactions of methyllithium , aUyllithium , aryllithiums" , and vinyllithium/potassium reagents " with oxiranes are reported (Scheme 36). 

Nonamethylcyclopentasilanyl-potassium, Me9Si5K, can be prepared via a mercury-potassium exchange reaction from bis(cyclopentasilanyl)mer-cury, (Me9Si5)2Hg, which is obtained by the reaction of hydro-cyclopenta-silane with (t-Bu)2Hg (Scheme 22) (87). This potassium reagent offers a new route to permethylated polycyclic polysilanes. 

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. ... 

Crotylboronic esters (2-butenylboronates) are thermally stable and isolable compounds at room temperature and undergo nearly quantitative additions to aldehydes. The required crotylboronic esters may be prepared by reaction of the crotyl potassium reagents derived from cis- or trans-2-butene with n-butyllithium and potassium tert-butoxide followed by addition of the appropriate trialkyl borates. ... 

S123 Seralyzer potassium reagent strips, package circular 6/85. 

Figure 4 Structures of allyl- and crotyl-magnesium, -lithium and -potassium reagents as determined by isotopic perturbation studies. The magnesium reagent (a) exists as a o-structure and the potassium (b) and lithium (c)...

Hexxol Sunset Yellow FCF Supra 865 Hexamine (potassium reagent) 1481... 

A few studies have been carried out on coupling of alkynyl borones. The stable methoxy(alkynyl)borate complex 158 was prepared in situ by the treatment of B-methoxy-9-borabicyclo[3.3.1]nonane (157) with alkynyllithiums or potassium reagents, and used directly for the coupling with halides to afford a variety of the disubstituted alkynes sueh as 159 [72,73]. 

Among very few examples of the reactions of organo-sodium or -potassium reagents with halogenophosphines appearing in the past year are reports of the synthesis of new bulky pyrazolylphosphines" and 2-diphe-nylphosphinomalonate esters. ... 

Normally, however, alkyl sodium and potassium reagents metallate alkenes rather than add to them. Organolithium or Grignard reagents are also unreactive towards C—C multiple bonds. Vigorous conditions are needed to cause organolithiums to add to 1-alkenes unless the latter are activated e.g. 

The potassium reagent (1) will deprotonate simple alkenes to give allylic anions. Subsequent reaction with a chloroborane results in the allylic borane, which, in turn, can be converted to an allyl alcohol (eq 4). ... 

The reaction is driven by the precipitation of the alkali metal halide. In THF, it has been shown that KI typically precipitates cleanly providing the best results. Thus, the combination of potassium reagents (see above) with the iodides has been widely employed in this route. Limitations of this reaction route include the limited solubility of the alkaline-earth metal iodides and potassium derivatives, requiring the need for ethereal solutions. This need for polar solvents may result in ether cleavage reactions. 

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