Potassium methide

Ah initio calculations on the competing metallo-dehydrogenation and nucleophilic addition reactions of organomethides with crotonaldehyde dimethylacetal reveal that addition to the double bond predominates in the case of lithium whereas this is only slightly preferred in the case of potassium methide the effect of R OK on deaggregation of RLi oligomers and on weakening C —Li+ interaction has been discussed.104... 

There are compounds in which a carbon atom participates in both ionic and covalent bonding. When methyl chloride, CHsCl, reacts with potassium, potassium methide, CH3K, is formed. 

Potassium methide is a crystalline, ionic solid in which there are three covalent C—H bonds, and one ionic bond between the [tCHj]" anion and the K" cation. Such carbon anions, called CAR8ANI0NS, are almost invariably bonded only to the highly electropositive elements of group IR or 2R. With the less electropositive metallic elements, carbon forms a covalent bond. For example, dimethylmercury, HjC—Hg—CH, is a typical covalent compound (b.p. 96°C). Carbanions are formed as very reactive intermediates in some organic reactions. 

Solvent-extracted delignified beech wood pulp was treated with potassium tertiary butoxide, then with quinone methides at 25 °C or 45 °C (Figure 4.13). Following reaction, extensive solvent extraction was then performed, and the modified flour was pressed to form a disc, which was then exposed to C. versicolor or G. trabeum. No indication of biological attack was found (Loubinoux etal., 1992). 

The facile electrocyclic ring closure of ortho-quinone methides provides a convenient strategy for the synthesis of 277-chromenes. Oxidation of ortho-allylic phenols using DDQ or potassium dichromate is a popular method for the formation of 277-chromenes, via ortho-quinone methide intermediates, and is discussed in detail in the preceding volumes (Scheme 6) <1984CHEC, 1996CHEC-II>. 

Chromenes, o-Allylphenols are oxidized to 3-chromenes by potassium dichromate dissolved in benzene in the presence of Adogen 464 in yields of 45-83%. 0 -Quinone methides are postulated intermediates. These heterocycles are also obtained on oxidation of o-allylphenols with DDQ, but in this case ether is preferable to benzene (82-90% yield cf. 2, 116). 

An example of this overall approach in elucidating novel bioactivation pathways is highlighted with studies on the potassium channel opener, maxipost (BMS-204352) (Figure 6.2), which undergoes a unique P450-mediated bioactivation reaction in rats, dogs, and humans to yield an electrophilic o-quinone-methide intermediate, which covalently binds to albumin in vivo in animals and human.33-34 Acidic hydrolysis of plasma collected after intravenous administration of [14C]-BMS-204352 to rats and human led to the characterization of a... 

Potassium hexacyanoferrate(III) Quinone methids from phenols 910. OH... 

The blue colour formed on oxidation of variegatic acid (73) by oxidases or by alkaline potassium ferricyanide is due to the formation of delocalised hydroxyquinone methide anions of type (77) (Scheme 10) (607). The electronic spectrum of anions such as (77) is in close accord with that of the blue anion (78) generated by oxidation of catechol in the presence of Meldrum s acid (700). Due to its nature as a vinylo-gous carboxylic acid a substantial proportion of the hydroxyquinone methide (77) is present in the form of its anion even at neutral pH. 

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