Potassium ter -butoxide

Oxabicyclo[4.1.0]hept-3-enes with a bromo substituent in position 2 can be converted to oxepins 11 by reaction with an appropriate base such as potassium ter+butoxide or triethylamine (see the experimental procedures for the preparation of the parent system in Houben-Weyl, Vol. 6/ld, pi78 and Vol. 6/4, p462).12,156,157 Usually the reaction products are mixtures of oxepin 11 and benzene oxide 12. In the case of ZerZ-butyl 7-oxabicyclo[4,1.0]hept-3-ene-2-carboxylate, the equilibrium lies completely on the benzene oxide side 12a.158... 

An interesting variation appears when furan reacts with the allenic carbene generated by the action of potassium ter-butoxide upon l-bromo-3,3-dimethylallene. Though the yield is only 9%, one product is reasonably assigned a structure (Scheme 52) that could hardly be approached by way of a cyclopropane intermediate. The authors comment that in an allenic carbene in the singlet state two electrons will be accommodated in the sp... 

When methyl a-chloro-a-[l-(diphenylmethyleneamino)cyclopropyl]acetate was treated with lithium diisopropylamide or potassium ter/-butoxide, spirocyclopropane 18 was obtained in 47 and 70 /o yield, respectively. This transformation is likely to proceed via the norcaradiene intermediate 17, the result of intramolecular cyclopropanation of an aromatic nucleus. In this case, there is evidence for a carbene- rather than an MlRC-type cyclopropanation step. 

The reaction of an alkene with bromo(phenyl)carbene (or carbenoid), generated from di-bromo(phenyl)methane (benzal bromide) and potassium ter -butoxide, afforded 1-bromo-l-phenylcyclopropanes (Houben-Weyl, Vol. 4/3, pp232-233, and Vol. E19b, p998). The reactions were carried out by shaking all components (10- 12 equivalents of an alkene) in a sealed tube at ca. 25°C for 50-70 hours. ... 

Bromo-1 -(2,5-dibromo-3-thienyl)cydopropanes were prepared via the addition of bromo(2,5-dibromo-3-thienyl)earbene, generated from 2,5-dibromo-3-dibromomethylthiophene and potassium ter/-butoxide, to an alkene. ... 

The synthesis of 1,1-diiodocyclopropane is carried out via addition of diiodocarbene (car-benoid) to alkenes the carbene, in turn, is generated from iodoform and a base. The process is realized using phase-transfer catalysis,(33% or 50%aqueous sodium hydroxide and a quaternary ammonium salt, typically benzyltriethylammonium chloride, as a catalyst) or in the presence of potassium ter/-butoxide in /ert-butyl alcohol 25,127,128 g... 

The seleeted products prepared using iodoform/potassium ter -butoxide are listed in Table 34. 

Addition of dibromocarbene to bicyclo[3.2.1]octa-2,6-diene, under the basic conditions used to generate the carbene, yielded 3,4-dibromobicyclo[3.3.l]nona-2,7-diene (27), which was de-hydrobrominated on treatment with potassium ter/-butoxide in dimethyl sulfoxide, to give 3-bromotricyclo[3.3.1.0 ]nona-3,6-diene (28). ... 

Table 4. Alkylidenetriangulanes by Dehydrobromination of 1-Alkyl-l-bromocyclopropanes with Potassium ter/-Butoxide in Dimethyl Sulfoxide ...

The reaction of 1,2-dichloro-l-raethylcyclopropane (1, X = Cl) with potassium ter/-butoxide presents the possibility of a double elimination followed by an addition to the highly strained methylenecyclopropene intermediate. Thus, when the reaction is carried out in tetrahydrofuran at a low temperature, l-tcrt-butoxy-2-methylenecyclopropane (2) is isolated in 37% yield. A similar reaction i n dimethyl sulfoxide at 18 - 20 °C gave 33 % of the same product. 

With bulkier alkoxides, e. g. potassium ter/-butoxide in fcrr-butyl alcohol or potassium (4-chlorophenyl)dimethylcarbinolate, a-bromo ketone 16 is converted into rra x-2,3-di-/cr/-butyl-cyclopropanone (17). Addition of methanol or 2-propanol to cyclopropanone 17 at 25 °C gives a fast addition reaction resulting in hemiacetal 21, which slowly undergoes ring opening at 80 °C in methanol to give a-methoxy ketone 22 (R = Me). ... 

Aldehydes react in accordance with the preceding scheme only if branched at the -position. According to Rapson et al.133, benzaldehyde reacts with an aqueous-alcoholic solution of chloroform containing sodium hydroxide. Straight-chain aliphatic and nitrated aromatic aldehydes react with chloroform in an anhydrous mixture of tetrahydrofuran and tert-butyl alcohol containing potassium ter/-butoxide at 0° to —20°, yields being good.134... 

In a seminal work published in 1977, Ito and coworkers described the behaviour of a DL generated by reaction of 8-caprolactone in the presence of catalytic potassium ter<-butoxide (0.5—2% mol) in THF at... 

Although Schdllkopf and Schrdder initially reported using only -butyllithium and potassium ter/-butoxide in their generation of metallo-isocyanides (4) from alkyl isocyanides (1), lithium diisoproylamide (LDA) has subsequently proven a useful complement to these bases, allowing for the metalation of ethyl isocyanide and other alkyl isocyanides that are not effectively metalated with n-butyllithium. ... 

Another means to enhance the basicity of n-butyllithium consists in using it in a mixture with potassium ter-butoxide. Here again, coordination of lithium with the oxygen atom of t-BuOK breaks the tetrameric cluster ( -BuLi)4, which leads to the formation of a very active monomer. Alternatively, it is possible to add a cosolvent such as hexamethylphosphoramide (HMPA) to a commercial solution of n-butyl-lithium in hexane, which has the same effect as TMEDA indicated above. Finally, one can also evaporate the hexane solvent and add a more polar solvent such as ether with or without cosolvent. Note that n-butyllithium is not a bulky base, and thus it also often reacts as a nucleophile. In these cases, it is necessary to prepare a bulky base by reaction of n-butyllithium with a bulky amine such as diisopropylamine, bis(trimethylsilyl)amine or tetramethylpiperidine. 

Wagner-Meerwein rearrangement, double 29, 686 Wagner rearrangement, vinylogous 29,987 Water (s. a. imder Potassium ter -butoxide)... 

Lithium acetylide reacts very smoothly with ketones. For example, it combines rapidly with 2-norbomanone (bicyclo[2.2.1]heptan-2-one) to give 1-exo-ethynyl-2-e (io-norbomanol. If camphor is the substrate the ethinyl groups enters on the endo face. The addition of acetylene onto ketones can even be brought about by catalytic amounts of potassium ter/-butoxide. ... 

The ratio of enolate vj. vinylalkoxide approximates 3 1 when an alkyllithium is used as the reagent. The addition of potassium ter/-butoxide raises the selectivity to about 9 1 [1101] Obviously the increase in metal-oxygen bond polarity makes it energetically more rewarding to produce the resonance-stabilized enolates. Unfortunately the [1,4]- V5. [l,2]-selectivity diminishes again when a secondary or tertiary alkyl migrates. The ratio amounts to 2 5 for neat lithium compounds and 3 2 for potassium/lithium mixed metal species... 

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