Potassium with electrophiles

Addition of nitroalkanes 402 (R = Me, Bu, Ph etc.) to methyl acrylate without a solvent in the presence of Amberlyst-21 gives good yields of the esters 403436. An analogous reaction with electrophilic acetylenes, e.g. dimethyl acetylenedicarboxylate, in the presence of potassium fluoride and tetrabutylammonium chloride yields adducts 404 as mixtures of geometrical isomers437. 

The cleavage of the Si—Si bond in the 9,10-disilanthracene 8 dimer by lithium metal in THF allows the synthesis of a dimetalated species 9 (Scheme 4)42. The reaction can be quenched at this point with electrophiles such as methyl iodide. Extended reaction times in the presence of excess metal produced 9,10-dimetalla-9,10-disilaanthracene 10 (M = Li). The corresponding potassium derivative 10 (M = K) was obtained directly from 8 upon treatment with excess metal. These 1,4-dimetalla species 10 have been used to synthesize a variety of civ-substituted disilaanthracene derivatives42. 

Treatment of indole (pKa - 17) with strong bases such as butyl lithium, Grignard reagents, or metal hydrides produces the corresponding indolyl anion, which reacts with electrophiles either on nitrogen or at the C3 position. With lithium, sodium, or potassium as counterion the indolyl anion tends to react on nitrogen, as in the preparation of 7.35. However, with magnesium as the counterion the intermediate has an essentially covalent rather than ionic structure, and reaction tends to occur at the C3 position, as in the preparation of 7.36. 

Frechet et alJ62a] further investigated the functionalization of the poly(benzyl ether) dendritic superstructure or framework (Scheme 5.19). For example, treatment of monoalcohol 70 [G-4]-OH fourth tier alcohol) with a 1 3 mixture of n-butyllithium and potassium f< r/-pentoxide (THF, hexane, - 85 °C) gave the polypotassium salt 75. Quenching with electrophiles that included D20, Me3SiCl, Ci8H37Br or C02 provided the functionalized dendrimer 76. However, electrophilic addition was not site-specific, although multisite substituted dendrimers were produced. 

The simplest member of the series, the 2,4-pentadienyl metallo species, has been shown by NMR studies,132 133 to adopt either a W-shape or a U-shape conformation with the metal being lithium or potassium, respectively, when both are dissolved in tetrahydrofuran.134 136 The W-form is adopted by the 2,4-pentadienylpotassium when the organometallic species is generated in liquid ammonia137 or in paraffinic suspension.138 This has also been confirmed by the stereochemistry of the products formed after reaction with electrophiles.134,135,138,139... 

Imidazoline-2-thiones are reduced by potassium metal in THF forming stable carbenes (imidazol-2-ylidenes) 756 that react very readily with electrophiles (see also Section 3.4.1.8.5). 

The same chiral auxiliary has also been used for the stereoselective synthesis of arene-chromium complexes treatment of an aromatic aminal with chromium hexacarbonyl gives the corresponding complex with high diastereomeric excess. This protocol was recently applied in a total synthesis of (—)-lasubine (eq 4). A successful application of 1,2-diaminocyclohexane (as its IR,2R enantiomer) as a chiral auxiliary is illustrated by the di-astereoselective alkylation of the potassium enolate of bis-amide (3) with electrophiles such as benzyl bromide to give bis-alkylated products with excellent diastereoselectivity (eq 5). Lower levels... 

Several papers have dealt with electrophilic attack at the amide nitrogen of the unsubstituted benzisoselenazol-3(27T)-one. Alkylation using KOH and alkyl or allyl halide or halocarboxylic ester gave 2-substituted benzisoselenazol-3(27T)-ones <1991CZ135, 1989BSB395> and the reaction has synthetic value. 6-[Benzisoselenazol-3(27T)-one]-/3-cyclodextrin, designed as an artificial enzyme, was prepared by reaction of benzisoselenazol-3(2//)-one potassium salt with 6-iodo-/3-cyclodextrin (/3-CD-6-I) (Scheme 12) <2002CAR1309>. 

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