Continuous Flow Synthesis of a Key 1,4-Benzoxazinone Intermediate via a Nitration/Hydrogenation/Cyclization Sequence

The preparation of a functionalized 4H-benzo-[1,4]-oxazin-3-one was completed via a three-step nitration/hydrogenation/cyclization sequence. The unstable nature of the nitro and amino intermediates, in addition to the hazards associated with the nitration of organic compounds in general, makes this procedure exceedingly difficult to perform on industrial scale. To overcome these limitations, we have developed a fully integrated continuous protocol in which the aromatic starting material (2,2-difluoro-2-(3-fluorophenoxy)-<i>N</i>,<i>N</i>-dimethylacetamide) is subjected to an initial continuous flow dinitration using 20% oleum in combination with 100% HNO₃ (2.5 equiv) using a microstructured device heated to 60 °C. This was followed directly by continuous flow hydrogenation of the dinitrointermediate over a Pd/C fixed bed catalyst at 45 °C. The resulting air-sensitive diamino derivative was then directly cyclized to the desired 6-amino-2,2,7-trifluoro-4H-benzo-[1,4]-oxazin-3-one target compound via an acid-catalyzed cyclization step at 80 °C using a tubular reactor. Uninterrupted continuous flow processing was achieved by integrating liquid–liquid membrane separation technology and the inline removal of excess of hydrogen gas using gas permeable tubing into the process. The overall product yield for the continuous flow process was 83%, a significant increase compared to yield reported for the batch process (67%)

Planar Biphenyl-Bridged Biradicals as Building Blocks for the Design of Quantum Magnets

We have synthesized and investigated a new biphenyl-4,4′-bis­(nitronyl nitroxide) radical with intermediately strong antiferromagnetic interactions. This organic biradical belongs to a family of materials that can be used as a building block for the design of new quantum magnets. For quantum magnetism, special attention has been paid to coupled <i>S</i> = ¹/₂ dimer compounds, which when placed in a magnetic field, can be used as model systems for interacting boson gases. Short contacts between the oxygen atoms of the nitronyl nitroxide units and the hydrogen atoms of the benzene rings stabilize a surprisingly planar geometry of the biphenyl spacer and are responsible for a small magnetic interdimer coupling. The strength of the antiferromagnetic intradimer coupling constant <i>J</i>/<i>k</i>_B = −14.0 ± 0.9 K, fitting the experimental SQUID-data using an isolated-dimer model. The deviations from the isolated-dimer model are attributed to a small interdimer coupling <i>J</i>′/<i>k</i>_B, on the order of 1 K, consistent with the crystal structure

Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure

Electro-oxidation of the quinoidal bisdithiazole BT in dichloroethane in the presence of [Bu₄N]­[GaBr₄] affords the 1:1 radical ion salt [BT]­[GaBr₄], crystals of which belong to the trigonal space group <i>P</i>3. The packing pattern of the radical cations provides a rare example of an organic kagome basket structure, with <i>S</i> = 1/2 radical ion chains located at the triangular corners of a trihexagonal lattice. Magnetic measurements over a wide temperature range from 30 mK to 300 K suggest strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i>_b ∼ 30 K, but reveal no anomalies that would be associated with magnetic order. These observations are discussed in terms of the symmetry allowed magnetic interactions within and between the frustrated layers

Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure

Electro-oxidation of the quinoidal bisdithiazole BT in dichloroethane in the presence of [Bu₄N]­[GaBr₄] affords the 1:1 radical ion salt [BT]­[GaBr₄], crystals of which belong to the trigonal space group <i>P</i>3. The packing pattern of the radical cations provides a rare example of an organic kagome basket structure, with <i>S</i> = 1/2 radical ion chains located at the triangular corners of a trihexagonal lattice. Magnetic measurements over a wide temperature range from 30 mK to 300 K suggest strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i>_b ∼ 30 K, but reveal no anomalies that would be associated with magnetic order. These observations are discussed in terms of the symmetry allowed magnetic interactions within and between the frustrated layers

Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure

Electro-oxidation of the quinoidal bisdithiazole BT in dichloroethane in the presence of [Bu₄N]­[GaBr₄] affords the 1:1 radical ion salt [BT]­[GaBr₄], crystals of which belong to the trigonal space group <i>P</i>3. The packing pattern of the radical cations provides a rare example of an organic kagome basket structure, with <i>S</i> = 1/2 radical ion chains located at the triangular corners of a trihexagonal lattice. Magnetic measurements over a wide temperature range from 30 mK to 300 K suggest strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i>_b ∼ 30 K, but reveal no anomalies that would be associated with magnetic order. These observations are discussed in terms of the symmetry allowed magnetic interactions within and between the frustrated layers