More Sustainable Approaches for the Synthesis of N-Based Heterocycles

Phase separation as a strategy toward controlling dilution effects in macrocyclic Glaser-Hay couplings

Macrocycles are abundant in numerous chemical applications, however the traditional strategy for the preparation of these compounds remains cumbersome and environmentally damaging; involving tedious reaction set-ups and extremely dilute reaction media. The development of a macrocyclization strategy conducted at high concentrations is described which exploits phase separation of the catalyst and substrate, as a strategy to control dilution effects. Sequestering a copper catalyst in a highly polar and/or hydrophilic phase can be achieved using a hydrophilic ligand, T-PEG(1900), a PEGylated TMEDA derivative. Similarly, phase separation is possible when suitable copper complexes are soluble in PEG(400), a green and efficient solvent which can be utilized in biphasic mixtures for promoting macrocyclization at high concentrations. The latter phase separation technique can be exploited for the synthesis of a wide range of industrially relevant macrocycles with varying ring sizes and functional groups.

Multicomponent reactions for the synthesis of heterocycles

Multicomponent domino reactions (MDRs) serve as a rapid and efficient tool for the synthesis of versatile heterocycles, particularly those containing structural diversity and complexity, by a one-pot operation. These reactions can dramatically reduce the generation of chemical wastes, costs of starting materials, and the use of energy and manpower. Moreover, the reaction period can be substantially shortened. This Review covers recent advances on multicomponent domino reactions for the construction of five-, six-, and seven-membered heterocyclic skeletons and their multicyclic derivatives.

Mechanistic insights into Cu(I)-catalyzed azide-alkyne "click" cycloaddition monitored by real time infrared spectroscopy

A designed ligand-accelerated Cu(I)-catalyzed cycloaddition (CuAAC) reaction was monitored for the first time by real time infrared analysis technique based on ATR-FTIR principles. Principal components analysis (PCA) and two-dimensional correlation spectroscopy (2Dcos) results showed that the consumption of alkyne and azide took place successively followed by the formation of the product 1,2,3-triazole, and a 1:1 complex of two reactants would be formed in the reaction process. The rate-determining step of the CuAAC reaction was also experimentally confirmed for the first time to be the transition of azide-alkyne 1:1 complex to the preproduct 1,2,3-triazole. Our results are in good conformity with the current catalytic mechanism proposed by Sharpless et al. according to DFT calculation results.

Expanding the family of mesoionic complexes: donor properties and catalytic impact of palladated isoxazolylidenes

Abnormal isoxazolylidene complexes, a new subclass of mesoionic complexes containing an isoxazolium-derived carbene type ligand, have been synthesised via oxidative addition and compared to structurally related mesoionic complexes by using (31)P NMR spectroscopy as a convenient probe for their donor ability and in catalytic cross-coupling reactions.