Current Organic Chemistry - Volume 18, Issue 4, 2014

This review concerns the role of microwave irradiation in the synthesis of heterocycles starting from carbohydrates. This topic has received increasing interest owing to the wide variety of heterocyclic compounds as biologically significant chiral natural products or drugs, and products for industrial application, which cover nearly all aspects of carbohydrate chemistry. In particular, the possibility of employing microwave irradiation as a source of energy together with simple low-molecular-weight carbohydrates, as attractive chiral raw materials, has led to the production of low-cost and eco-friendly heterocycles within the framework of a green chemistry approach. Moreover, the employment of small amounts of solvents or solvent-free systems with solid supports, enables reaction completion in much shorter times under more environmentally clean conditions and preparation of the target compounds on the scale of grams, without the risk of any major hazards. The many possible combinations of skeletal, building block, and stereochemical diversity elements make this a highly attractive synthetic approach. This review covers the period from the first utilization of microwave irradiation until 2012 and includes the syntheses of (i) heterocycles linked directly or via a tether to carbohydrates, (ii) heterocycles annulated with carbohydrates, (iii) heterocycles from carbohydrates via hetero-Diels-Alder (HDAR) and Diels-Alder (DAR) reactions, or via 1,3-dipolar cycloadditions, with particular regard to the “click reaction” (CuAAC), (iv) iminosugars, and (v) 5-hydroxymethylfurfural.

In this article we present (+)-3-carene as a valuable source for the synthesis of compounds with various odoriferous properties. Described compounds consist of carane, bicyclo[3.1.0]hexane, and gem-dimethylcyclohexane system in their structure. Olfactory comparative analysis with regard to the structure has been discussed. Fragrance of molecules varies from different fruit notes to floral and woody. Future prospects regarding application of biocatalysts towards synthesis of compounds with olfactory properties are briefly discussed and the synthesis details are also presented to show the simplicity of the preparation of some valuable fragrant molecules. The major part of our study has been previously described only in patents that in our opinion makes this paper a valuable data source of olfactory characteristics of low-molecular compounds derived from (+)-3-carene.

The radical TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radical) and its derivatives are well-established catalysts for oxidation processes, and now used extensively in organic synthesis and industrial applications as a mild, safe, and economical alternative to heavy metal reagents as highly selective oxidation catalysts. In this review, we attempt to fully review the recent advances in the syntheses of TEMPO and its derivatives as well as their applications in recent years. The synthesis of TEMPO and its derivatives are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis, particularly focusing on the formation of C-C, C-O, C=O, C-N, and C=N bond. Simultaneously, the oxidation of alcohols to their corresponding carbonyl compounds also is commented briefly. The last section discusses the application of the TEMPO-catalyzed reactions in the total syntheses of natural products.

Porphyrin is a kind of versatile chemically sensitive materials for application in chemical sensors. Recently, a variety of porphyrinic polymer membranes have been developed as gas sensors. Most of them are based on the photoluminescent or photoexcited state quenching of porphyrin dyes. Many porphyrinic gas sensors are composed of porphyrin or its derivatives immobilized on gas permeable polymer membranes. In this review, we present the state-of-art of various porphyrinic polymers for optical gas sensors, including those for oxygen (O2), hydrogen chloride (HCl), nitric oxide (NO) and carbon dioxide (CO2).

Attempts to induce stereoselectivity in the conjugate addition to the α,β-unsaturated acceptors have been investigated by numerous research groups, classically through the use of either a chiral acceptor or chiral donor component in the reaction. The asymmetric Michael addition catalyzed by chiral catalysts has been extensively proven and established to be a powerful synthetic tool for especially a range of asymmetric syntheses of natural products and various heterocyclic systems. This review covers the recent reports and further applications of this methodology in the formation of carbon-carbon bond between or within functionalized and sensitive substrates which provides new opportunities, mainly in the total synthesis, medicinal and process chemistry, nanotechnology and chemical biology.

The reaction of a series of symmetric and unsymmetric triaminobenzene derivatives with proton as electrophile has been studied. The formation of both Wheland complex (C-H salt) and N-H salt in relative amount depending on the experimental conditions has been observed. In the case of the attack of the proton on the nitrogen atom, the 1H and 13C NMR spectra showed the equivalence of three aromatic protons (and related carbon atoms) of the adduct thus indicating that salification occurs on a non-defined nitrogen atom. This behavior can be explained hypothesizing motion of the proton from a nitrogen atom to another in a motion that could not permit to define the protonation site. On the contrary, X-ray diffraction analysis on crystals of the NH salts reveals that in the solid state the proton is situated in a well-defined position.