Microwave synthesizer

The microwave acceleration of Ugi condensations on a sohd support have been utilized in the synthesis of an 18-membered targeted hbrary of a-acylamino amides [60], Irradiation of the four components, immobilizing the amine on TentaGel S RAM, for 3-5 min in a single-mode microwave synthesizer gave the products in moderate to excellent yields and high purity (Scheme 7). 

Microwave irradiation has been used to accelerate the Gewald reaction for the one-pot synthesis of N-acyl aminothiophenes on solid support [67]. A suspension of cyanoacetic acid Wang resin 35, elemental sulfur, DBU and an aldehyde or ketone 36 in toluene was irradiated for 20 min at 120 °C in a single-mode microwave synthesizer (Scheme 13). Acyl chloride 37 was added, followed by DIPEA, and the mixture was irradiated for 10 min at 100 °C. After cooling to room temperature, the washed resin was treated with a TEA solution to give M-acylated thiophenes 38 in 81-99% yield and purities ranging from 46-99%. 

The rapid synthesis of 4-thiazolidinones by the MCR of an amine, aldehyde and mercaptoacetic acid has been developed under microwave-assisted conditions [73-75]. Irradiation of the three components in ethanol at 120 °C in the presence of molecular sieves [73] or in toluene at reflux under atmospheric conditions [74] in a single-mode microwave synthesizer gave the... 

Alkynyl ketones 157 were also used for the synthesis of pyrimidines 159 by reacting amidines in acetonitrile at 120 °C in a dedicated microwave synthesizer without the requirement of additional purification (Scheme 56) [104]. 

Microwave synthesized mesoporous Tin MFI as efficient catalyst for Baeyer-Villiger Oxidation of cyclic ketones... 

Scheme 4.18 Microwave syntheses in l-alkyl-3-methylimidazolium ionic liquids (see text for references).

I. T. Badejo (Bayer Corporation). Microwave Syntheses oe Quinacri-DONES, 6,13-DlHYDROQUINACRIDONES AND 6,13-QuiNACRIDONEQUINONES AT Moderate Temperatures. Eur. Patent Application EP 905,199,1999 (US Patent Application 63,128, 20 Apr 1998) Chem. Abstr 1999, 130, 253670q. 

Thermally stable. Silica can withstand temperatures of over 200 °C and is suitable for use in microwave synthesizers. 

A library of 4 chain extended homopolymers and 12 diblock copoly(2-oxazoline)s was prepared from 2-methyl, 2-ethyl, 2-nonyl, PheOx in a very short period of time [90]. The CROP was initiated by methyl tosylate and performed in acetonitrile at 140 °C in a single-mode microwave synthesizer. A total number of 100(50 + 50) repeating units was incorporated into the respective polymer chains. The concentration of the solutions and predefined polymerization times for each monomer and comonomer are summarized in Table 11. 

A library of 30 triblock copolymers was synthesized from 2-methyl, 2-ethyl, 2-nonyl, and PheOx in a single mode microwave synthesizer [92]. The polymers exhibited narrow PDI values and showed slight deviations from the targeted monomer ratio of 33 33 33. The design of the experiments is shown in Scheme 12. 

A microwave-assisted Fischer indole synthesis under solvent-free conditions with Montmorillonite K10 clay modified with zinc chloride was employed in a key step of the synthesis of analogues of the cytostatic natural product, Sempervirine (Scheme 3.6)8. A dedicated laboratory microwave synthesizer was utilised. 

Fang, X., Hutcheon, R. and Scola, D.A., Microwave syntheses of poly(epsilon-caprolactam-co-epsilon-caprolactone), /. Polym. Sci., Part A Polym. Chem., 2000, 38,1379. 

Pivonka and Empfield of AstraZeneca Pharmaceuticals describe the continuous acquisition of Raman spectra of an amine or Knoevenagel coupling reaction in a sealed micro-wave reaction vessel at elevated temperatures and pressures.57 A microwave synthesizer was modified to accommodate a non-contact Raman probe. This approach helps... 

A mixture of phenacyl chloride 1 (0.46 g, 3 mmol), aldehyde 2 (0.64 g, 6 mmol), ammonium acetate (1.55 g, 20 mmol) and glacial acetic acid (10 ml) in w-PrOH (20 ml) in the presence of molecular sieves (4 A) was irradiated for 5-10 min in a self-tunable CEM microwave synthesizer at 90 °C (Scheme A.7). After the reaction had been cooled to room temperature, the solvent was removed under vacuum and the residue was crystallized from ethanol to give 2,4,6-triphenyl-3,5-diazabicyclo[3.1.0]hex-2-ene 3 as colorless crystals. Melting point 155-156°C. 

Microwave treatment is widely used to prepare various refractory inorganic compounds and materials (double oxides, nitrides, carbides, semiconductors, glasses, ceramics, etc.) [705], as well as in organic processes [706,707] pyrolysis, esterification, and condensation reactions. Microwave syntheses of coordination and organometallic compounds, discussed in this chapter, are presented in a relatively small number of papers in the available literature. As is seen, the use of microwaves in coordination chemistry began not long ago and, due to the highly limited number of results, these works can be considered as a careful pioneer experimentation, in order to establish the suitability of this technique for synthetic coordination chemistry. 

Scheme 10 Carbonylative microwave syntheses of C2-symmetric HIV-1 protease inhibitors from protected starting aryl halides...

In view to increase in number of microwave synthesized organic reactions and advancement in technology most companies developing microwave instruments for commercial applications offer a variety of diverse reactor platform with different degrees of sophistication with respect to automation, database capabilities, safety features, temperatures and pressures monitoring and vessel design. 

Reaction containment during microwave syntheses is relatively straightforward, but some limitations are imposed, as vessel materials must be both mechanically robust and microwave transparent. Ambient and elevated pressure vessels may be constructed from standard laboratory glassware, polytetrafluoro-ethylene (PTFC), or other microwave-transparent polymers, although vessels specifically tailored for microwave synthesis are commercially available. 

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