Potassium tert-butoxide radical

The same group recently disclosed a related free radical process, namely an efficient one-pot sequence comprising a homolytic aromatic substitution followed by an ionic Homer-Wadsworth-Emmons olefination, for the production of a small library of a,/3-unsaturated oxindoles (Scheme 6.164) [311]. Suitable TEMPO-derived alkoxy-amine precursors were exposed to microwave irradiation in N,N-dimethylformam-ide for 2 min to generate an oxindole intermediate via a radical reaction pathway (intramolecular homolytic aromatic substitution). After the addition of potassium tert-butoxide base (1.2 equivalents) and a suitable aromatic aldehyde (10-20 equivalents), the mixture was further exposed to microwave irradiation at 180 °C for 6 min to provide the a,jS-unsaturated oxindoles in moderate to high overall yields. A number of related oxindoles were also prepared via the same one-pot radical/ionic pathway (Scheme 6.164). 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

Distribution of spin density in the framework of trianion-radicals allows determining whether or not there is some conjugation between substituents at different sites. For example, reduction of dinitro spiro(indoline-benzopyran) with potassium tert-butoxide in DMSO proceeds according to Scheme 1.40 (Alberti et al. 1995). 

The major oxidation product isolated was anthracene, perhaps formed in part from the hydroperoxide (I). However, significant amounts of potassium superoxide accompanied the anthracene. This result suggests that the major source of anthracene involved the oxidation of the dianion. In pure DMSO in the presence of excess potassium tert-butoxide, a trace of oxygen converts 9,10-dihydroanthracene, 9,10-dihy-drophenanthrene, or acenaphthene to the hydrocarbon radical anions. These products are apparently formed in the oxidation of the hydrocarbon dianions. 

Figure 7. First derivative ESR spectra of radical anions observed in dimethyl sulfoxide solutions of potassium tert-butoxide. Top, autoxidation product of diphenylamine. No signal was observed in the absence of oxygen. Middle, autoxidation of 4-hydroxy-diphenylamine. Bottom, spontaneous reduction product of mono-anil of p-benzoquinone.

Molybdenum-based catalysts are highly active initiators, however, monomers with functionalities with acid hydrogen, such as alcohols, acids, or thiols jeopardize the activity. In contrast, ruthenium-based systems exhibit a higher stability towards these functionalities (19). An example for a molybdenum-based catalyst is (20) MoOCl2(t-BuO)2, where t-BuO is the tert-butyl oxide radical. The complex can be prepared by reacting M0OCI4 with potassium tert-butoxide, i.e., the potassium salt of terf-butanol. 

A tandem radical sequence was observed when the indole amide 120 was treated with tributylstannyl radical [81]. The initially formed aryl radical is proposed to undergo a 1,5-hydrogen atom abstraction to form an a-amido radical en route to the cyano spiroindolines 121a and 121b. Treatment with potassium tert-butoxide and oxygen in THF gave the C-3 spirooxindole in modest yield. 

Di-0-benzyl-3,4-0-isopropylidene-D-mannitol was ring closed to afford a 9 1 cis/trans mixture of 189 in high yield by (Swern) oxidation and radical cyclization of the dialdehyde using samarium iodide in fcrf-butanol. The cis-diastereoisomer was selectively converted into a cis-cyclic sulfate which underwent cleavage upon treatment with potassium tert-butoxide to afford a cyclo-... 

In 1970, Bunnett and Kim reported a new nucleophilic aromatic substimtion reaction the S l mechanism (substitution, radical-nucleophilic, first order) [77-80]. Nine years later, Bunnett [81] and Beugelmans [82,83] independently discovered the application of the S l reaction to the synthesis of indoles (Scheme 10). In Bunnett s work (equation 1) the aeetone enolate (and others) was generated from acetone and potassium tert-butoxide (tert-butyl alcohol) in the presence of potassium amide in liquid ammonia [81]. Indoles 16 to 18 were also prepared by Bard and Bunnett. Beugelmans and Roussi employed a similar... 

The absence of radical products in the reaction of Scheme IV, and the formation of only a limited amount of product in the perester decomposition (Scheme HI) which could have arrived by a non-radical path (via could be explained in at least two ways. The two pair species, one from perester and the other from the pairing of ions, could differ in that the ion sources contribute potassium and triflate ions which could be included in an ion aggregate, possibly more likely to give ionic products than is the unperturbed sulfonium—tert-butoxide pair. Further work will be required to confirm or deny this explanation. The associated uncertainty remains a defect in the experiment. 

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