Bases Potassium fluoride-Alumina

A solventless Suzuki coupling reaction has been developed using both thermal and microwave-assisted methods. A potassium fluoride-alumina mixture is utilized along with palladium powder. The KF acts as a base. ... 

Benzylation of alcohols using Potassium Fluoride-Alumina and benzyl bromide in acetonitrile at room temperature is effective. Silver oxide in DMF is yet another base system. Of particular interest in carbohydrate applications is the reaction of benzyl bromide with carbohydrate derivatives which have been pretreated with tin reagents. Thus it is possible to benzylate an equatorial alcohol in the presence of an axial alcohol (eq 1) and also to selectively benzylate an anomeric hydroxy through Di-n-butyltin Oxide. ... 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

Recently, this method has been modified by application of a milder base (KF/AI2O3, alumina, coated with potassium fluoride) (04SC1425). N,N-Diethylpropin-l-amine 79 can be substituted for nitriles 27, so N,N-disubstituted pyrans 131 can be obtained (73JHC165) (Scheme 46). 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

The preparation of oxazolines from p-hydroxy amides and SOCI2 via the corresponding p-chloro amides under basic conditions is well known and has been discussed earlier. Potassium fluoride on alumina has been reported as a mild alternative to the aqueous or alcoholic bases that are commonly used. The reaction is typically carried out in acetonitrile or tetramethylene sulfone and moderate to good yields of oxazolines and oxazines can be obtained as shown in Scheme 8.29. 

The same author also found the combination of potassium fluoride on alumina to be the most efficient in the phenylation reaction of aroyl chlorides. Five different bases and different power outputs were screened to find the optimal conditions31 (Scheme 2.5). 

A base comprising of alumina impregnated with potassium fluoride in the presence of benzyltriethylammonium chloride as a catalyst has recently been recommended for the cyclo-propanation of alkenes with chloroform, e.g. formation of 1, the yield without the catalyst was 30%. ... 

Amino-3-cyano-thiophenes or 2-amino-thiophene-3-esters result from this route, generally conducted as a one-pot process, involving a ketone that has an a-methylene, ethyl cyanoacetate or malononitrile, sulfur, and morpholine. Various improvements to the original procedure include using microwave irradiation on solid snpport, or with potassium fluoride on alumina as the base, or solvent-free,and using morpho-lininm acetate in excess morpholine for aryl alkyl ketones. 

Potassium fluoride on alumina is sometimes used as a base.23 It may be that the fluoride ion displaces some surface hydroxyl from the alumina to produce some potassium hydroxide. Lithium chloride, bromide, and iodide on silica... 

Potassium fluoride on alumina is a solid base.69 (It forms potassium hydroxide by exchange of fluoride for hydroxyl groups on the surface of the alumina.) An example of its use is given by Reaction 6.21.70 It has also been used without solvent in the Tishchenko reaction of benzaldehyde to give benzyl benzoate if 94% yield.71 Potassium fluoride on an aluminum phosphate molecular sieve was a weaker base in the isomerization of 1 -butene.72... 

The preparation of 2-nitro alcohols was also achieved by reaction of equimolar amounts of nitroal-kanes and aldehydes in the presence of alumina-supported potassium fluoride without solvent (equation 12). A peculiar feature of diis method were reactions performed with aromatic aldehydes, such as benz-aldehyde and furaldehyde, which allowed preparation of the corresponding 2-nitro alcohols without dehydration of these into nitroalkenes, as observed when nitroaldol reactions were performed with organic bases in homogeneous medium or with alumina alone. 

Pharmacologically significant naturally occurring 2-aroylbenzofurans are easily obtainable in the solid state from a-tosyloxyketones and salicylaldehydes in the presence of a base such as potassium fluoride doped alumina (67) using microwave irradiation (Scheme 24). 

Supported reagents which can perform partial oxidations have been reported for example, the solid base KF-alumina (potassium fluoride supported on alumina) has been found to oxidise fluorene to fluorenone very effectively (Figure 16.22) [27]. 

I, 3-Diketones are alkylated in the 2-position in the absence of base via their cobalt(ii) or nickel(ii) complexes. Similarly, use of potassium fluoride on Celite or alumina in place of base gives high yields of the 2-alkyI derivatives. ... 

An exception to the otherwise general use of an organic base is the employment of potassium fluoride on alumina with microwave heating [55]. A range of cyclic ketones, p-keto-esters and aldehydes were used successfully - an example is shown in Scheme 34. 

Potassium fluoride coated on alumina has been shown to be an effective and practical base for the usual Williamson-type synthesis of crown ethers from polyethylene glycols and polyethylene glycol ditosylates [equation (23)],giving yields comparable to standard methods. 

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