A solid-state NMR study of ring-chain tautomerism in 1,3- O,N-Heterocycles

Abstract

The solid-state 13C CP/MAS nmr spectra of nineteen tetrahydrooxazines and oxazolidines have been recorded to determine their preferences for the ring or chain tautomeric form in the solid state. The chain form is preferred for those cases in which <80% of the ring tautomer is found in solution. The ring form is exclusively found only in derivatives with ⪢93% preference for the ring tautomer in solution. In one case the solid-state reaction converting the open chain to the ring was observed to take place over a time-scale of several days. An investigation of the tautomeric equilibrium in tetrahydrooxazines and oxazolidines in the solid state is reported.