Montmorillonit K 10 clay

The oxidation has also been accomplished with Claycop (montmorillonite K-10 clay supported cupric nitrate). The reaction of 96 to 102 was complete in 1.5-7 h with 81-93% yields. The time can be reduced to 5-10 minutes using ultrasound with minimal effect on yields. The major limitation of this protocol was the observation that only R = aryl gave product. Oxidation of 4-alkyl substituents was inert to these conditions with recovery of starting 96. 

A solvent-free strategy for the synthesis of thiazoles involved mixing of thioamides with a-tosyloxy ketones in a clay-catalyzed reaction (Scheme 7). The typical procedure entailed mixing of thioamides and in situ produced a-tosyloxy ketones with montmorillonite K-10 clay in an open glass container. The reaction mixture was irradiated in a microwave oven for 2-5 min with intermittent irradiation and the product was extracted into ethyl acetate to afford 2-substituted thiazoles in 88-96% yields [8]. 

The common microwave oven has been brought into the laboratory. Using special Teflon reaction vessels, components are mixed together, the vessel sealed and put into the microwave oven. Reaction times are greatly accelerated in many reactions, and reactions that took hours to be complete in refluxing solvents are done in minutes. Benzyl alcohol was converted to benzyl bromide, for example, using microwaves (650 W) in only 9 min on a doped Montmorillonite K-10 clay. This is a growing and very useful technique. 

Alkyl aryl ketones can be converted to arylacetic acid derivatives in an entirely different manner. The reaction consists of treatment of the substrate with silver nitrate and I2 or Br2, ° or with thallium nitrate, MeOH, and trimethyl orthoformate adsorbed on Montmorillonite K-10 clay, an acidic clay. ... 

The l,3-oxazin-2-ones and 1,3-oxazine-2-thiones previously synthesized were used to prepare various N- and O-heterocyclic systems fused with 1,3-oxazine rings.172 For example, furan-l,3-oxazin-2-one or furan-l,3-oxazine-2-thiones (190a,b) and pyran-l,3-oxazin-2-ones or pyran-l,3-oxazine-2-thiones (190c,d) were prepared in very good yields, ranging from 83% to 90%, by montmorillonite K-10 clay-catalyzed cyclodehydration of 189a,b and 189c,d, respectively (Scheme 35). 

The preparation of imines, enamines, nitroalkenes and N-sulfonylimines proceeds via the azeotropic removal of water from the intermediate in reactions that are normally catalyzed by p-toluenesulfonic acid, titanium(IV) chloride, or montmorillonite K 10 clay. A Dean-Stark apparatus is traditionally used which requires a large excess of aromatic hydrocarbons such as benzene or toluene for azeotropic water elimination. 

MW-expedited dehydration reactions using montmorillonite K 10 clay [70] (Schs. 6.20 and 6.21) or Envirocat reagent, EPZG [71] (Schs. 6.20 and 6.21) have been demonstrated in a facile preparation of imines and enamines via the reactions of primary and secondary amines with aldehydes and ketones, respectively. The generation of polar transition state intermediates in such reactions and their enhanced... 

A simple montmorillonite K 10 clay surface is one among numerous acidic supports that have been explored for the Beckmann rearrangement of oximes (Scheme 6.27) [54]. However, the conditions are not adaptable for the aldoximes that are readily dehydrated to the corresponding nitriles under solventless conditions. Zinc chloride has been used in the above rearrangement for benzaldehyde and 2-hydroxyacetophe-none, the later being adapted for the synthesis of benzoxazoles. 

Scheme 6.25 Pinacol-pinacolone rearrangement on AI3+-montmorillonite K 10 clay.

A facile method for the oxidation of alcohols to carbonyl compounds has been reported by Varma et al. using montmorillonite K 10 clay-supported iron(III) nitrate (clayfen) under solvent-free conditions [100], This MW-expedited reaction presumably proceeds via the intermediacy of nitrosonium ions. Interestingly, no carboxylic acids are formed in the oxidation of primary alcohols. The simple solvent-free experimental procedure involves mixing of neat substrates with clayfen and a brief exposure of the reaction mixture to irradiation in a MW oven for 15-60 s. This rapid, ma-nipulatively simple, inexpensive and selective procedure avoids the use of excess solvents and toxic oxidants (Scheme 6.30) [100]. Solid state use of clayfen has afforded higher yields and the amounts used are half of that used by Laszlo et al. [17,19]. 

A solvent-free synthesis of flavones has been achieved that simply involves the MW irradiation of o-hydroxydibenzoylmethanes adsorbed on montmorillonite K 10 clay for 1-1.5 min. A rapid and exclusive formation of cyclized flavones occurs in good yields (Scheme 6.41) [140], The intramolecular Michael addition of o-hydroxy-... 

With a-hydroxy ketones and their related tosyloxy derivatives. The imidazo [2,T ]thiazole 364 was prepared by acetic acid-catalyzed cyclocondensation of 2-hydroxy-l,2-diphenyl-ethanone with thiophenyl-substituted 2-aminothiazole 363 (Equation 163) <2002MI110>. Under MW irradiation and in the presence of montmorillonite K-10 clay, a mixture of a-tosyloxyketones 365 and 2-imidazolidinethione led to the substituted 5,6-dihydro-imidazo[2,l- ]thiazoles 366 (Equation 164) <1998J(P1)4093>. When using a-tosyloxyacetophenone, prepared by reaction of acetophenone with [hydroxyl(tosyloxy)iodo]benzene (HTIB), 5-aminopyrazole 367 could be converted to imidazo[l,2- ]pyrazole 368 in basic medium (Equation 165) <2005JHC209>. 

Bromination of uracil 63 with NBS in tetrabutylammonium bromide gave 5-bromouracil 64 in 78% yield after 2h, but with microwave assistance in the presence of acidic montmorillonite K-10 clay the reaction time was cut to just 4min and the yield was increased to 96% <200581103>. Cytosine reacted similarly <200581103>. 

The Lewis acid-catalyzed condensation of a,/3-unsaturated ketones 277 with amides 278 furnished 2,4,6-trisubsti-tuted-6//-l,3-oxazines 279. An environmentally benign solvent-free version of this process, based on the application of montmorillonite K-10 clay and a brief microwave irradiation, provided oxazines 278 in higher yields than in the conventional solution-phase method (Equation 26) <2004BCJ2265>. 

To activated montmorillonite K-10 clay (2 g) in a 100-mL Erlenmeyer flask was added a mixture of freshly distilled phenol (0.50 g, 5.3 mmol) and recrystallized p-methoxycinnamic acid (0.94 g, 5.3 mmol) dissolved in CH2CI2 (5 mL) along with one drop of concentrated H2SO4. The solvent was evaporated and the resultant free-flowing solid placed on a silica bath and subjected to microwave irradiation at 640 W for 10 min. Dichloromethane (20 mL) was added, the reaction mixture filtered and the filtrate washed with saturated NaHC03 solution, brine and dried over Na2S04. Evaporation of the solvent in vacuo yielded the product, 1.05 g (82%). 

A mixture of benzaldehyde la (106 mg, 1 mmol) and 2-aminopyridine 3a (94 mg, 1 mmol) was irradiated in an unmodified household microwave oven for 1 min (at full power of 900 W) in the presence of montmorillonite K-10 clay (50 mg). After addition of benzyl isocyanide 2a (117 mg, 1 mmol), the reaction mixture was further irradiated successively (2 min) at 50% power level for a duration of 1 min followed by a cooling period of 1 min. The resulting product was dissolved in dichlorometliane (2x5 mL) and the clay was filtered off. The solvent was removed under reduced pressure and the crude product was purified either by crystallization or by passing it through a small bed of silica gel using EtOAc-hexane (1 4, v/v) as eluent to afford 4a. 

Montmorillonite K-10 clay (1.0 g) is mixed with la (0.1 g, 0.45 mmol) in solid state using a pestle and mortar or alternatively with a solution of la in dichloro-methane (2 mL). The adsorbed material is transferred to a glass tube and is inserted in an alumina bath (alumnia 100 g, mesh 65-325, Fisher scientific bath 5.7 cm diameter) inside the microwave oven. The compound is irradiated for 1.5 min (the temperature of alumina bath reached 110°C at the end of this period) and the completion of the reaction is monitored by TLC examination. The product is extracted into dichloromethane (2x15 mL) and clay is filtered off. Removal of the solvent under reduced pressure affords 2-phenyl-1,2,3,4-tetraliydro-4-quinolone 2a, in 80% yield, mp 148-150 °C. 

Keywords aldehyde, ketone, amine, montmorillonite K-10 clay, microwave irradiation, imine, enamine... 

To an equimolar (1 mmol) mixture of benzaldehyde 2a (106 mg) and aniline la (93 mg) placed in an open glass container, montmorillonite K-10 clay (20 mg) is added and the reaction mixture is irradiated in a microwave oven at full power for 3 min. Upon completion of the reaction, as followed by TLC examination, the product is extracted into dichloromethane (3 x 10 mL). Removal of the solvent under reduced pressure affords the benzylidene aniline 3a in 98% yield. 

A mixture of p-chlorobenzaldehyde If (0.7 g, 5 mmol), aniline 2f (0.455 g, 5 mmol) and montmorillonite K-10 clay (0.1 g) contained in a 25-mL beaker was placed in an alumina bath inside the microwave oven and irradiated for 2 min. The in situ generated Schiff s base was mixed thoroughly with freshly prepared NaBH4-clay (5.0 mmol of NaBH4 on 1.72 g of reagent) and water (1 mL). The reaction mixture was again irradiated for 30 s (65 °C). Upon completion of the reaction, monitored on TLC, the product was extracted into methylene chloride (3x 15 mL). The removal of solvent under reduced pressure provided pure /V-phe-nyl-p-chlorobenzylamine 4f in 90% yield. The identity of the product was confirmed by formation of the hydrochloride salt, mp 209-211 °C. 

A mixture of epoxide 1 (1 mmol), amine 2 (1 mmol) and montmorillonite K-10 clay (0.2 g) was placed in a Teflon container with a screw cap. Then the mixture was irradiated with high power (900 W) in a conventional microwave oven for 1 min. After the mixture was cooled to room temperature, it was washed with di-chloromethane (2xl0mL). The solvent was evaporated and the products were identified. 

Desilylation of phenols or alcohols in the presence of montmorillonite K-10 clay 1 mmol of silyl ether was placed in a 5-mL beaker, and 0.1 g of activated montmorillonite K-10 clay was added. The beaker was placed in a 50-mL Teflon container and irradiated in a microwave oven (900 W) for 1 to 5 min. The progress of the reaction was monitored by GLC. After completion of the reaction, the product was extracted with ether or CH2C12, filtered, and the solvent was evaporated under reduced pressure to yield the corresponding phenol. 

Phenols react with cinnamyl compounds via an intermolecular condensation/cyclization providing a reliable method for the construction of dihydrocoumarins. Montmorillonite K-10 clay can catalyze the condensation/cyclization reaction of phloroglucinol and cinnamoyl chlorides to provide a high-yielding route to dihydrocoumarins (Equation 416) <2001S2247>. 

Two new heterogeneous catalysts have been prepared by exchanging a Montmorillonite K-10 clay with dilute solutions of RhCb and MnlNOsls, respectively. These catalysts are effective for the synthesis of /ra r-aziridines (e.g., 602) from imines (e.g., 600) and methyl diazoacetate (Scheme 146) <1997CC1429>. 

Thiazoles have been readily obtained from thioamides and a-tosyloxy-ketones, catalyzed by montmorillonite K-10 clay under MW irradiation, in excellent yields. These compounds are very difficult to synthesize under conventional heating conditions (Scheme 8.25). ... 

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