Solvent-free synthesis of heterocyclic compounds using microwaves

An expeditious synthesis of benzoxazine-2-thione c-nucleosides Via Cu(OTf)2-mediated dehydrazinative beta-glycosylation

A novel expeditious synthetic protocol for 1,3-benzoxazine-2-thione C-nucleosides via Cu(OTf)2-mediated dehydrazinative beta-glycosylation of 4-hydrazino-2H-benz[e]-1,3-oxazine-2-thiones with unprotected D-ribose is reported.

6-Amino-4-(4-chlorophenyl)-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile ethanol solvate

The title compound, C₁₃H₇ClN₄O·C₂H₆O, was synthesized by the reaction of 4-chloro­benzaldehyde, malononitrile and 10% sodium hydroxide solution in an aqueous medium. In the crystal structure, the crystal packing is stabilized by inter­molecular N—H⋯N, O—H⋯O and N—H⋯O hydrogen bonds.

Microwave-assisted organic synthesis and transformations using benign reaction media

A nonclassical heating technique using microwaves, termed "Bunsen burner of the 21st century", is rapidly becoming popular and is dramatically reducing reaction times. The significant outcomes of microwave (MW)-assisted green chemistry endeavors, which have resulted in the development of synthetic protocols for drugs and fine chemicals synthesis that are relatively more sustainable, are summarized. The use of emerging microwave-assisted chemistry techniques in conjunction with greener reaction media is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief historic account of our own experiences in developing MW-assisted organic transformations, which involve various benign alternatives, such as solid-supported reagents, and greener reaction media, namely, aqueous, ionic liquid, and solvent-free, for the synthesis of various heterocycles, coupling reactions, oxidation-reduction reactions, and some name reactions are described. Synthesis of Heterocycles. The synthetic chemistry community has been under increased pressure to produce, in an environmentally benign fashion, the myriad of heterocyclic systems required by society in a short span of time, and one of the best options to accelerate these synthetic processes is to use MW technology. The efficient use of the MW heating approach for the synthesis of various heterocyclic compounds in aqueous and solvent-free medium is discussed. Organic Named Reactions. The application of MW chemistry for various named reaction such as the Prins reaction, the Suzuki reaction, the Heck reaction, the Aza-Michael reaction, Trost's gamma-addition, and the Cannizzaro reaction are summarized. Synthesis and Application of Ionic Liquids. Ionic liquids (ILs), being polar and ionic, in character couple with MW irradiation very efficiently and are, therefore, ideal MW-absorbing candidates for expediting chemical reactions. MW-assisted solvent-free synthesis and application of ILs are discussed. Oxidation-Reduction Reactions. MW protocols using mineral oxides such as alumina, silica, and clay to immobilize reagents on such solid supports have been extensively explored under "dry" media conditions. Various solvent-free examples of oxidation reactions are discussed that involve mixing of neat substrates with clay-supported iron(III) nitrate (clayfen) or iodobenzene diacetate (IBD) as an oxidant; some interesting MW reduction protocols using borohydrides are also discussed. Protection-Deprotection Reactions. The protection and deprotection of alcohols and amines are common events in multistep organic syntheses. Various protection and deprotection protocols under MW irradiation are discussed, including tetrahydropyranylation and (benzyloxycarbonyl) (Cbz)-protection, which are the most frequently employed methods.

Greener and expeditious synthesis of bioactive heterocycles using microwave irradiation

The utilization of green chemistry techniques is dramatically reducing chemical waste and reaction times as has recently been proven in several organic syntheses and chemical transformations. To illustrate these advantages in the synthesis of bioactive heterocycles, we have studied various environmentally benign protocols that involve greener alternatives. Microwave (MW) irradiation of neat reactants catalyzed by the surfaces of recyclable mineral supports, such as alumina, silica, clay, or their "doped" versions, enables the rapid one-pot assembly of heterocyclic compounds, such as flavonoids, related benzopyrans, and quinolone derivatives. The strategy to assemble oxygen and nitrogen heterocycles from in situ generated reactive intermediates via enamines or using hypervalent iodine reagents is described. Examples of multicomponent reactions that can be adapted for rapid parallel synthesis include solventless synthesis of dihydropyrimidine-2(1H)-ones (Biginelli reaction), imidazo[1,2-a]annulated pyridines, pyrazines, and pyrimidines (Ugi reaction). The relative advantages of greener pathways, which use MW irradiation and eco-friendly aqueous reaction medium, for the synthesis of various heterocycles, such as N-aryl azacycloalkanes, isoindoles, 1,3-dioxane, 1,3,4-oxadiazole, 1,3,4-thiadiazole, pyrazole, and diazepines, are also summarized.

Rapid and efficient microwave-assisted copper(0)-catalyzed ullmann coupling reaction: general access to anilinoanthraquinone derivatives

[structure: see text]. The synthesis of anilinoanthraquinones 3a-z was achieved by a new, Cu(0)-catalyzed, microwave-assisted Ullmann coupling reaction of bromaminic acid (1) with aniline derivatives 2a-z in phosphate buffer. Good to excellent isolated yields were obtained within only 2-20 min at 80-120 degrees C and 40-100 W. The new procedure provides the first general access to anilinoanthraquinones, furnishing a number of previously inaccessible compounds. It is superior to classical methods in all aspects, including yields, reaction time, and versatility.

An efficient and simple aqueous N-heterocyclization of aniline derivatives: microwave-assisted synthesis of N-aryl azacycloalkanes

[reaction: see text] An efficient and clean synthesis of N-aryl azacycloalkanes from alkyl dihalides and aniline derivatives has been achieved using microwave irradiation in an aqueous potassium carbonate medium. The phase separation can simplify the product isolation and reduce usage of volatile organic solvents.

Diversity-Oriented Synthesis of 3-Iodochromones and Heteroatom Analogues via ICl-Induced Cyclization

The ICl-induced cyclization of heteroatom-substituted alkynones provides a simple, highly efficient approach to various 3-iodochromones and analogues. This process is run under mild conditions, tolerates various functional groups, and generally provides chromones in good to excellent yields. Subsequent palladium-catalyzed transformations afford a rapid increase in molecular complexity and a convenient preparation of a wide range of functionally substituted chromones, furans, and polycyclic compounds. Iodothiochromenones and iodoquinolinones are also prepared by similar ICl-induced cyclizations.

Aqueous N-Heterocyclization of Primary Amines and Hydrazines with Dihalides: Microwave-Assisted Syntheses of N-Azacycloalkanes, Isoindole, Pyrazole, Pyrazolidine, and Phthalazine Derivatives

[reactions: see text] The synthesis of nitrogen-containing heterocycles from alkyl dihalides (ditosylates) and primary amines and hydrazines via a simple and efficient cyclocondensation in an alkaline aqueous medium that occurs under microwave irradiation is described. This improved greener synthetic methodology provides a simple and straightforward one-pot approach to the synthesis of a variety of heterocycles, such as substituted azetidines, pyrrolidines, piperidines, azepanes, N-substituted 2,3-dihydro-1H-isoindoles, 4,5-dihydropyrazoles, pyrazolidines, and 1,2-dihydrophthalazines.