Development of a General Protocol To Prepare 2H-1,3-Benzoxazine Derivatives

Abstract

A practical synthesis and detailed development process of 2H-1,3-benzoxazine derivatives catalyzed by aldimine and trifluoromethanesulfonic acid is described. A broad range of substrates with diverse steric and electronic properties were explored. Aliphatic/aromatic/heteroaromatic substrates all proceed well under conditions which have been optimized into a robust, scalable process.

Enantioconvergent 6π Electrocyclization Enabled by Photoredox Racemization

“…49 Current synthetic methods for accessing this core are specific to elbasvir 50,51 or restricted to racemic or achiral derivatives. 52,53 This work expands the utility of O'Donnell's Schiff base derivatives. While these compounds are extensively exploited as chiral ligands and have been a staple of amino acid synthesis, 54,55 substituted derivatives are difficult to functionalize in their ketimine form, 15 and have rarely been employed in fully catalytic oxidative processes.…”

“…The 2 H -1,3-benzoxazine core is present in several bioactive compounds, such as fungicides, the potassium channel opener TCV-295, and a cytotoxic agent targeting human colon adenocarcinoma (Scheme C) . Current synthetic methods for accessing this core are specific to elbasvir , or restricted to racemic or achiral derivatives. , This work expands the utility of O’Donnell’s Schiff base derivatives. While these compounds are extensively exploited as chiral ligands and have been a staple of amino acid synthesis, , sterically congested α-substituted derivatives are difficult to functionalize in their ketimine form, and have rarely been employed in fully catalytic oxidative processes. , …”

Reactive diluent strategy for general benzoxazine to achieve high performance thermoset via a combination of styrene and glycidyl methacrylate

“…Accordingly, considerable efforts have been devoted to solve this problem, and the approaches can be divided into three classes: (i) exploration of liquid benzoxazines, 28–31 (ii) dilution using organic solvents, 32–36 (iii) application of benzoxazine powder, 18 and (iv) mixing of two benzoxazine resins 37–40 . For instance, Lochab et al 40 synthesized a low‐viscosity benzoxazine using cardanol as raw material, showing a viscosity of 145 mPa s at 43°C.…”

“…This inability in molecular design suggests the dilemma between the liquidation of benzoxazine monomer and high performance of the resulting polymeric resin. On the other hand, solvents such as acetone, 32 chloroform, 33 ether, 34 butanone, 35 and methylene chloride 36 were also tried to dissolve solid benzoxazines for curing process. However, such methodologies are troubled by the requirement of removing solvent, countermeasures to the hazard volatiles, and prevention of pore defects caused by residual solvent 42 …”