Ketyl-type anions

Pestalotiopsin A and 6-epitaedolidol are structurally related caryophyllene-type sesquiterpenes. In 2003, Procter reported the use of a Sml2-mediated 4-exo-trig carbonyl-alkene cyclisation to construct the core of pestalotiopsin A.57 Treatment of cyclisation substrate 33 with Sml2 in THF, MeOH and 2,2,2-trifluoroethanol gave cyclobutanol products 34 and 35 in good yield and with moderate diastereoselectivity. The major diastereoisomer is believed to arise from a cyclisation in which coordination to the silyl ether group directs addition of the ketyl radical anion to the alkene (Scheme 7.17).57... 

Acetylenic Compounds.— The reductive cyclization of acetylenic ketones with naphthalene radical-anions has been studied for a variety of 4,5-secocholest-3-yn-5-one analogues (139). Products vary with structural type three examples are illustrated in Scheme 5. Results are interpreted in terms of initial electron transfer from the reagent to form a ketyl radical-anion, followed by intramolecular radical attack on the triple bond. ... 

Allyl (27, 60, 119-125) and benzyl (26, 27, 60, 121, 125-133) radicals have been studied intensively. Other theoretical studies have concerned pentadienyl (60,124), triphenylmethyl-type radicals (27), odd polyenes and odd a,w-diphenylpolyenes (60), radicals of the benzyl and phenalenyl types (60), cyclohexadienyl and a-hydronaphthyl (134), radical ions of nonalternant hydrocarbons (11, 135), radical anions derived from nitroso- and nitrobenzene, benzonitrile, and four polycyanobenzenes (10), anilino and phenoxyl radicals (130), tetramethyl-p-phenylenediamine radical cation (56), tetracyanoquinodi-methane radical anion (62), perfluoro-2,l,3-benzoselenadiazole radical anion (136), 0-protonated neutral aromatic ketyl radicals (137), benzene cation (138), benzene anion (139-141), paracyclophane radical anion (141), sulfur-containing conjugated radicals (142), nitrogen-containing violenes (143), and p-semi-quinones (17, 144, 145). Some representative results are presented in Figure 12. 

Several types of radical anions are known with the unpaired electron or the charge or both on atoms other than carbon. Important examples are semiquinones197 (20) and ketyls 98... 

As described above, with the combination of appropriate lanthanide reducing agents, solvents, and substrates, almost all types of the key intermediates involved in the reduction of ketones have been isolated and structurally characterized (Scheme 21), such as the one-electron reduction product (ketyl radical 21), its reversible coupling product (pinacolate 24), hydrogen abstraction product (alkoxide 23) and further one-electron reduction product (ketone dianion 22), and the selective protonation products of the ketone anion (alkoxide 23 and eno-... 

Electron transfer involving ketyl anions of this type has been reported (7). In Figure 4a, Curve i is the transient spectrum observed 1 /xsec. after the pulse, from 3.34 mill acetophenone at pH 13. Curve ii is the spectrum obtained when 16.6-mM acetone is present in the solution. The maximum at 4400 A. is that of the acetophenone ketyl anion (21),... 

We now report a study of the structure of ionic species of a radical anion of the quinone methide type, a vinylog of a ketyl anion radical, using UV-visible and ESR spectroscopies in a wide range of concentrations. ... 

Acrylonit e is one of the most reactive monomers toward anionic catalysts. A wide range of initiators of this type has been used and include the alfin catalysts, alkoxides, butyUithium, metal ketyls, and solutions of alkali metals in ethers. In a number of anionic polymerizations, there is no termination reaction if pure reagents are used, and so-called living polymers are formed. Sudi living" systems are more difficult to observe in the case of acrylonitrile owing to the insolubility of the polymer in most of the usual solvents. It is possible to produce block co-polymers with acrylonitrile from other living" polymeric anions. 

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