Microwave-assisted organic synthesis in microstructured reactors

The coupling of microwave heating with microprocessing in continuous-flow reactors has been reviewed in various organic synthesis reactions. The fast growing field of microwave and microreactor technology has a significant impact on the development of fine chemicals industry. Both technologies offer not only the possibility of realizing many of the individual advantages integrated into one combined system, but also the potential of eliminating the major hurdle of a limited microwave penetration depth for large-scale chemical synthesis. Metal film-coated capillary microreactors allow creation of local hot spots to achieve temperatures far in excess of the solvent temperature, which accelerates chemical reactions under MW heating.     

Microwave-assisted organic synthesis using minivials to optimize and expedite the synthesis of diverse purine libraries

The new Personal Chemistry ultralow-volume (0.2-0.5 mL) minivials are shown to enable small-scale optimization and synthesis of purines at optimal reaction concentrations (0.1-0.4 M), thereby increasing the overall efficiency of this microwave-assisted library synthesis.     

微波辅助聚合物支载的有机反应

微波辐射下，聚合物支载的有机反应易于进行，操作简便，反应速率高，反应 时间短，产率高，纯度好，聚合物载体稳定，综述了微波辅助不溶性聚合物和可溶 性聚合物支载的有机反应。     

微波辅助合成邻羟基苯丁酮

利用微波辅助,以丁酸苯酯为原料,经Fries重排制备了邻羟基苯丁酮.通过单因素实验考察了反应时间、催化剂用量及反应温度对收率的影响,正交实验确定了最优工艺条件.结果表明,当n(催化剂):n(丁酸苯酯)=1.6,反应温度120℃,反应时间8 min时,丁酸苯酯完全转化,邻羟基苯丁酮收率45.0%.     

Microwave-assisted synthesis of corroles

The recently developed Gross's method for the synthesis of corroles has been modified and successfully applied to the preparation of new free base tris-aryl- and tris-pyrimidyl-corroles using solvent-free conditions and microwave irradiation. Compared to conventional heating, the microwave technique afforded an increase in corrole yields of ca. 30% and led to noticeably cleaner reaction mixtures. It is demonstrated that short reaction times and high temperatures are required to afford optimum yields.     

Microwave-assisted synthesis of metalloporphyrazines

The synthesis of metalloporphyrazines with enhanced yields directly from substituted maleonitriles is described. The one-step procedure involves tetramerization using hexamethyldisilazane, p-toluenesulfonic acid and DMF in a sealed tube under microwave irradiation. The reaction time has been drastically reduced from 24 h by classical oil-bath heating to just 15 min.     

Microwave-assisted synthesis of tetrahydroindoles

An efficient synthesis of tetrahydroindoles with different substituents in position 1 is described. Microwave-assisted aminolysis of 4-oxo-4,5,6,7-tetrahydrobenzofuran with different primary amines gives the corresponding tetrahydroindoles in few minutes. All attempts to use microwave dielectric heating to reduce the time required for preparation of 4-oxo-4,5,6,7-tetrahydrobenzofuran, starting from 1,3-cyclohexandione were on the other hand unsuccessful, demonstrating that in some cases, long time conventional heating may be superior to microwaves.     

Microwave-assisted organic synthesis of 3-substituted-imidazo[1,5-a]pyridines

3-Substituted-imidazo[1,5-a]pyridines were conveniently synthesized in two steps from commercially available picolinic esters under microwave irradiation conditions.     

Microwave-assisted solid-phase organic synthesis (MASPOS) as a key step for an indole library construction

[reaction: see text] Microwave-assisted solid-phase organic synthesis (MASPOS) has been demonstrated to significantly facilitate the Cu(II)- or Pd(II)-mediated ring closure of the resin-bound 2-alkynylanilides. Under microwave irradiation at 200 degrees C [for Cu(OAc)(2), NMP] or 160 degrees C [for Pd(MeCN)(2)Cl(2), THF] for 10 min, 1-acyl-2-alkyl-5-arenesulfamoylindoles were obtained, after cleavage from the resin, in 95-99% purities and in 65-82% overall yields via a 5-step synthetic sequence.     

Microwave-assisted Kornblum oxidation of organic halides

Microwave-assisted Kornblum oxidation is proved to be an effective way to obtain aldehyde and ketones from their corresponding chlorides. Under microwave irradiation, not only the reaction time was greatly decreased, due to avoiding the by-product, the yield was increased. It is noteworthy that the scope of the method was broadly expanded.     

Microwave-assisted organic synthesis: scale-up of palladium-catalyzed aminations using single-mode and multi-mode microwave equipment

Batch wise scale-up of Buchwald-Hartwig aminations under microwave irradiation has been investigated for the first time. Multi-mode (microSYNTH and MARS) (several vessels irradiated in parallel per batch) as well as single-mode (Discover) (one vessel irradiated per batch) platforms can be successfully used for this purpose with trifluoromethylbenzene (benzotrifluoride: BTF) as amination solvent. The obtained yields indicate a direct scalability in BTF for all the studied aminations. The Voyager equipment (based on a Discover platform) is the most convenient system since it allows an automatic continuous batch wise production without the necessity to manually load and unload reaction vessels.     

Microwave-assisted synthesis of sydnonyl-substituted imidazoles

3-Aryl-4-formylsydnones 1a-d react with symmetrical 1,2-dicarbonyl compounds, such as benzil (2a), 4,4′-dimethoxybenzil (2b), 4,4′-difluorobenzil (2c), and di-2-thienylethanedione (2d), in glacial acetic acid, using ammonium acetate as the ammonia source, to yield 4,5-diaryl-2-sydnonyl-substituted imidazoles 3a-6d under conventional heating. In a similar treatment, 4,5-diaryl-2-sydnonyl-1-substituted imidazoles 8a-10a can be prepared by the one-pot condensation of 3-(4-ethoxyphenyl)-4-formylsydnone (1d), benzil derivatives, ammonium acetate, and primary amines. However, such reactions, which take 1-3 days at high temperature under classical conditions, are completed successfully within a few minutes under microwave irradiation.     

Microwave-assisted synthesis of five-membered S-heterocycles

The development of new strategies for synthesis of five-membered S-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in sulfur-containing five-membered heterocyclic compounds synthesis is presented, focusing on the developments in the last 5–10 years. This contribution covers the literature concerning the total synthesis of five-membered S-heterocycles under microwave and combined effect of microwave and solid-phase.     

Microwave-assisted solid-phase synthesis of phthalimides

[reaction: see text] A traceless solid-phase synthesis of substituted phthalimides is proposed. The target compounds are obtained within minutes by a microwave-assisted cyclative cleavage in good yields and excellent purities.     

Microwave-assisted synthesis of medium-sized heterocycles

The development of new strategies for synthesis of medium-sized heterocycles has remained a highly attractive but challenging proposition. In the last few years, the application of microwave irradiation has greatly facilitated the construction of such heterocyclic ring systems through a myriad of different synthetic approaches. This feature article illustrates the progress made in the microwave-assisted synthesis of medium-sized heterocycles with an emphasis on examples describing the use of a dedicated microwave synthesizer.     

Microwave-assisted synthesis of photochromic fulgimides

A series of photochromic fulgimides have been successfully synthesized from their respective fulgides using microwave methodology. The yields of the fulgimides synthesized through this method, were an improvement over the thermal methods usually employed.     

Microwave-assisted total synthesis of tangutorine

A novel microwave approach to the synthesis of tangutorine is described. The key steps comprise a diastereoselective aldol condensation of monoprotected glutaraldehyde and a microwave-assisted Pictet–Spengler reaction. The stereochemistry of the tangutorine diastereomers obtained was determined by means of NOE-experiments.     

Microwave-assisted traceless synthesis of benzimidazolones

We have developed a microwave-assisted traceless rapid synthesis of benzimidazolones on polymeric supports. The key step in our approach involves an arylation of benzylammonia followed by treatment with N-chlorosulfonyl isocyanate and by subsequent hydrolysis to yield the corresponding primary ureas. Intramolecular cyclization of the resin-bound primary ureas under Pd-catalyzed condition followed by cleavage with TFA-H₂O provided the desired benzimidazolones with excellent yields and high purities. Except for step 4, the other reactions involved were performed completely within a few minutes under microwave exposure.     

苯并咪唑衍生物的微波辅助合成研究

开展了邻苯二胺与4-甲基苯甲醛、4-硝基苯甲醛及4-二甲氨基苯甲醛反应生成苯并咪唑衍生物的微波辅助合成研究。用高效液相色谱法(HPLC)测定其产率。结果表明:相同反应时间,在微波辅助条件下,生成苯并咪唑衍生物的反应产率均较常规加热条件下增大,并且芳醛对位上取代基吸电子能力越强,反应产率越高。     

Microwave-assisted synthesis of pyrrolidine derivatives

Microwave-assisted bismesylate amination is an efficient method of synthesizing pyrrolidine ring derivatives and provides a good to excellent product yield.