文摘
Abstract The synthesis and characterisation of three ammonium salts that are formed via a ring opening of a 2-oxazoline (i.e., a 4,5-dihydro-1,3-oxazole) are described. Compound 1, derived from 2-phenyl-2-oxazoline (Phox), was isolated as a major reaction product during an unrelated synthesis using Phox which was being carried out in the presence of NO3 − ions. The isolated compound is identified as the nitrate salt of the terminal ammonium ester [H3NCH2CH2OC(=O)Ph]+ (1). The X-ray crystal structure (C9H12N2O5) of 1 is revealed to be orthorhombic (space group Pna21) with a = 21.1304(8), b = 7.5975(2) and c = 6.8629(3)?. The analogous material 2a, obtained from the related oxazole 4,4-dimethyl-2-phenyl-2-oxazoline (MePhox) under identical conditions to that of 1, contains the [H3NCMe2CH2OC(=O)Ph]+ cation. The X-ray crystal structure (C11H16N2O5) of 2a is monoclinic with a = 6.1270(3), b = 6.3603(3), c = 16.1632(8)? and β = 90.662(3)o and of space group P21. Chiral derivative 2b, was isolated from a wet CH2Cl2/THF solution upon treatment of MePhox with (S)-mandelic acid. This material was shown to also contain the [H3NCMe2CH2OC(=O)Ph]+ cation, a lattice water molecule and an (S)-mandalate anion. The X-ray crystal structure of 2b (C19H23NO5¡¤H2O) is orthorhombic (space group P212121) with a = 6.4733(3), b = 11.4661(5) and c = 24.5791(11)?. One proposed mechanism by which all three materials are formed was first presented in seminal work by Deslongchamps. The compounds reported herein are representatives of a class of rarely isolated intermediates in heterocyclic ring opening reactions and they are also the first examples of (ω-ammoniumethyl)(aryl) esters to be structurally characterised.