Selective Synthesis and Structural Confirmation of 1,3‐Oxazines and Schiff Bases with Controllable Substitution Patterns

Abstract

Selective synthesis of 2,4‐diaryl‐2,3‐dihydro‐3H‐naphtho[1,2‐e]‐1,3‐oxazines and Schiff bases ((E)‐[1‐arylmethyl(benzylideneamino)]naphth‐2‐ols) that contain two identical or two different aryl substituents was achieved through one‐pot synthesis with ammonium acetate. From the proposed mechanism the dual role of ammonium acetate was identified. The synthesized products were characterized by 1H and 13C NMR spectroscopy, as well as FTIR and mass spectrometry. Crystal structures of the 1,3‐oxazines and Schiff base derivatives were examined. A notable feature is the conspicuous absence of strong donors (NH/OH) in any intermolecular hydrogen‐bonding scheme. Instead, packing is characterized by weak intermolecular CH⋅⋅⋅O, CH⋅⋅⋅π and CCl⋅⋅⋅π interactions, which lead to dimeric and zig‐zag one‐dimensional molecular patterns. The oxazine moiety of the tricyclic ring system predominantly adopts a half‐chair conformation. The present Mannich procedure is an environmentally benign and cost‐effective method for the preparation of industrially and pharmaceutically useful heterocyclic scaffolds.

Synthesis and Polymerization of Naphthoxazines Containing Furan Groups: An Approach to Novel Biobased and Flame-Resistant Thermosets

“…Interestingly, the compound Naft-H-Fu exhibits ringopen-chain tautomerism in solution. This fact has already been observed in a similar compound by Karthikeyan et al [29] and was attributed to a residual acidity of CDCl 3 . In the 1 H NMR spectra of this compound, it is possible to observe the signals attributed to Schiff's base at 8.40 ppm (-CH=N, marked as c) and 11.58 ppm (O-H, marked as d).…”