Microwave-Assisted Synthesis of Five-Membered O,N,N-Heterocycles

The development of new strategies for synthesis of five-membered O,N,N-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen and two nitrogen atoms containing five-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of five-membered O,N,N-heterocycles.     

Microwave-Assisted Synthesis of Six-Membered O-Heterocycles

The development of new strategies for synthesis of six-membered O-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen-containing six-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of six membered O-heterocycles.     

Nitrogen-Containing Six-Membered Heterocycles: Solid-Phase Synthesis

Solid-phase organic synthesis is a rapidly expanding area of synthetic chemistry that is being widely exploited in the search for new medicinally important compounds using combinatorial techniques. In recent decades, a large number of reports related to solid-phase synthesis of heterocycles have appeared because of the wide variety of their biological activity. In this review, we report the important role of solid-phase synthesis in the synthesis of nitrogen containing six-membered ring heterocycles.     

One-pot two-step tandem reactions for selective synthesis of pyrrolo[2,1-a]isoquinolines and dihydro-, tetrahydro-derivatives

A sequential one-pot two-step tandem reaction for selective and efficient synthesis of pyrrolo[2,1-a]isoquinoline and its dihydro- and tetrahydro-derivatives has been developed. The tandem reactions of isoquinoline, α-halogenated methylene compounds, aromatic aldehydes, and cyanoacetamide firstly give tetrahydropyrrolo[2,1-a]isoquinolines as main products. The corresponding pyrrolo[2,1-a]isoquinolines and dihydropyrrolo[2,1-a]isoquinolines can be obtained directly by controlling oxidation with DDQ. The mechanism of this tandem reaction involved the 1,3-dipolar cycloaddition of isoquinolinium ylide as the key step. A unique elimination of the amido group preferring to the cyano group has been observed.     

Synthesis of 3,4-disubstituted cinnolines by the Pd-catalyzed annulation of 2-iodophenyltriazenes with an internal alkyne

A simple and efficient synthesis of cinnolines was achieved by a palladium-catalyzed annulation methodology. 3,4-Disubstituted cinnolines are prepared via palladium-catalyzed annulation of 2-iodophenyltriazenes with an internal alkyne in moderate to good yields. Several internal alkynes are applicable to this reaction and it is compatible with a number of functional groups.     

A flexible synthesis of C-6 and N-1 analogues of a 4-amino-1,3-dihydroimidazo[4,5-c]pyridin-2-one core

A flexible route which enables access to derivatives of 4-amino-1,3-dihydroimidazo[4,5-c]pyridin-2-ones is described. Issues of selectivity, reaction safety, and low yields in original routes are overcome with the key improvements to the route, including a Negishi cross-coupling and use of a carbamate as a protecting group and intrinsic carbonyl source. The new route enables variation of C-6 and N-1 substituents.     

Synthesis and solid state study of pyridine- and pyrimidine-based fragment libraries

A library of pyridines and pyrimidines has been synthesised in excellent yields employing microwave and flow chemistry methodologies. Work-up bottlenecks have been facilitated substantially by the use of supported reagents and many of the final compounds have been studied in the solid state by single crystal X-ray diffraction.     

A new class of fluorescent dyes based on 1,3-benzodioxole and [1,3]-dioxolo[4.5-f]benzodioxole

We report on synthesis and photophysical properties of a new class of fluorescent dyes. They are characterized by large Stokes-shifts, long fluorescence lifetimes in organic solvents and a pronounced dependency of the fluorescence lifetime on the solvent polarity. Also worthy of note is the high bleaching stability. To provide access to biochemical and medical applications a series of derivatives were prepared, which exhibit specific reactivity towards different biologically relevant functional groups (carboxylic acids, amines, maleimides, N-hydroxysuccinimide esters). Furthermore, two alkynes were prepared, which could be used in ‘Click’ chemistry.     

The solar-chemical photo-Friedel-Crafts heteroacylation of 1,4-quinones

Photochemical reactions between 1,4-benzo- and 1,4-naphthoquinone and several heteroaromatic carbaldehydes were investigated under solar irradiation conditions. These reactions gave the corresponding heteroacylated hydroquinones in the range 71%-92% yield.     

Synthesis of (±)-6-oxa-3-azabicyclo[3.1.1]heptan-2-thione: a potential synthon for the preparation of novel heteroaryl-annulated bicyclic morpholines

The novel bridged bicyclic morpholinethione (±)-6-oxa-3-azabicyclo[3.1.1]heptan-2-thione (9) has been prepared in six steps. This conformationally restricted morpholinethione was prepared stereoselectively using straightforward chemistry and inexpensive starting materials. The key oxetane ring was formed via an intramolecular alkylation reaction.