The sphingolipid bases, D-erythro- and D-threo-sphingosines, are the target molecules that have been synthesized to demonstrate the efficiency of a new methodology to control both absolute and relative configurations in acyclic systems. Tubulysins are compounds of extraordinary potency, rapidly degrading the tubulin cytoskeleton, with tubulysin D being the most active tubulin-modifier known so far. Among other isonitriles, isocyanoacetate derivatives occupy an important place in the field of synthetic application and reaction diversity, which makes them strongly attractive objects for investigation. The unique multifunctional nature of isocyanoacetic acid derivatives opens up a range of exciting reactions, especially tandem/cascade processes for the synthesis of complex cyclic and macrocyclic systems. Multicomponent chemistry of isocyanoacetates is also a powerful instrument to access different classes of biochemically relevant compounds such as peptides, peptide molecules, and nitrogen heterocycles.

Isocyanoacetate derivatives: synthesis, reactivity, and application.

Isocyanides have long proved themselves to be irreplaceable building blocks in modern organic chemistry. The unique features of the isocyano group make isocyanides particularly useful for the synthesis of a number of important classes of nitrogen heterocycles, such as pyrroles, indoles, and quinolines. Several cocyclizations of isocyanides via zwitterions and radical intermediates as well as transition-metal-catalyzed syntheses of different types of heterocycles have recently been developed. Methods starting from isocyanides often have distinct advantages over alternative approaches to the same heterocycles because of their enhanced convergence, the great simplicity of most of the operations with them, and the great variety of isocyanides readily available for use. Isocyanides have also been used in some enantioselective syntheses of chiral heterocyclic compounds, including natural products as well as precursors thereof.

Isocyanides in the Synthesis of Nitrogen Heterocycles

Recent advances in the synthesis of pyrroles

Synthesis of tetrasubstituted imidazoles via α-(N-acyl-N-alkylamino)-β-ketoamides on Wang resin

Syntheses of soluble tetrabenzoporphyrins (TBP) and tetranaphtho[2,3]porphyrins (TNP), with multiple substituents in the conjugated aromatic rings but bearing no substituents in the meso-positions, is reported. Both types of porphyrins were obtained by direct aromatization of precursor porphyrins, annealed with either cyclohexene or dihydronaphthalene fragments. TBPs and TNPs possess powerful absorption bands in the near-infrared (λ = 610−710 nm, e = 100,000−300,000 M-1 cm-1) and exhibit strong luminescence. Free bases and Zn complexes fluoresce with quantum yields of up to 50%, whereas Pd and Pt complexes phosphoresce in solutions at ambient temperatures. Remarkably, the phosphorescence quantum yields of Pd and Pt TBPs reach as high as 20−50%, which places them among the brightest near-infrared phosphors known to date.

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Synthesis and Luminescence of Soluble meso-Unsubstituted Tetrabenzo- and Tetranaphtho[2,3]porphyrins

Benzyl esters of 5-unsubstituted pyrrole-2-carboxylic acids were prepared in excellent yields by the base-catalyzed condensation of benzyl isocyanoacetate with α-acetoxynitro compounds, or nitroalkenes, in refluxing tetrahydrofuran. These pyrrolic products are important intermediates in the synthesis of porphyrins and related compounds

Synthesis of Pyrroles from Benzyl Isocyanoacetate

Porphyrins with exocyclic rings. Part 12. Synthesis of meso,β-butano- and meso,β-pentanoporphyrins from cycloalka[b]pyrroles

Porphyrins with exocyclic rings. Part 23: Synthesis of porphyrins with large exocyclic rings—cyclohexadeca[b]pyrroles and porphyrins therefrom

Synthesis of Pyrroles from Benzyl Isocyanoacetate.

Knorr-type condensation of cyclododecanone, cyclopentadecanone, and cyclohexadecanone with phenylhydrazones derived from acetoacetate esters in the presence of zinc dust at elevated temperatures gave the corresponding large ring cycloalka[b]pyrroles in excellent yields. A cyclohexadeca[b]pyrrole was reacted with lead tetraacetate to give an acetate derivative, and this condensed with α-unsubstituted pyrroles in the presence of p-toluenesulfonic acid in acetic acid to give a series of related dipyrrolic structures. Hydrogenolysis of the benzyl ester protective groups, followed by ‘2+2’ condensations with dipyrrylmethane dialdehydes, gave unusual cycloalkanoporphyrins with 16-membered exocyclic rings. When an alkyl group is situated next to the carbocyclic ring, proton NMR spectroscopy indicates that the conformational mobility of the carbocyclic unit is severely restricted.

Jolie A. Bastian

Papers

Synthesis of Pyrroles from Benzyl Isocyanoacetate

Porphyrins with exocyclic rings. Part 12. Synthesis of meso,β-butano- and meso,β-pentanoporphyrins from cycloalka[b]pyrroles

Porphyrins with exocyclic rings. Part 23: Synthesis of porphyrins with large exocyclic rings—cyclohexadeca[b]pyrroles and porphyrins therefrom

Synthesis of Pyrroles from Benzyl Isocyanoacetate.

Porphyrins with Exocyclic Rings. Part 23. Synthesis of Porphyrins with Large Exocyclic Rings—Cyclohexadeca[b]pyrroles and Porphyrins Therefrom.