Formaldehyde benzoxazine synthesis

The polybenzoxazines (PBZs) provide a new class of phenolic resins that were first described by Ishida in 1998 (Ref. 15). Synthesis of the resins involves three components a phenol, a primary amine and formaldehyde. The first stage involves the formation of a multifunctional benzoxazine monomer Figure 23.30 a)). The monomer can then be ring-opened at elevated temperatures (160-220 C) to yield a polymeric stmcture (Figure 23.30(b)). 

The synthesis of a range of benzoxazines (35) from 34 using AgBp4 in anhydrous ether has been described . Thermolysis of these in a melt resulted in a retro-Diels-Alder reaction with loss of formaldehyde giving the azaxylylenes (36), which undergo spontaneous electrocyclization to give the 2-aIkyl-41/-3,1-benzoxazines (37) in excellent yields (Scheme 5). 

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