Structures of pyrrolo-1,3-heterocycles prepared from 3-aroylpropionic acid and cyclic aminoalcohols: an NMR and X-ray diffraction study

Abstract

By the reaction of 3-(4-chlorobenzoyl)propionic acid 1 with 1,2- and 1,3-bifunctional compounds, new condensed heterocycles have been prepared. Thus, the reaction of 1 with hydrazine gave the pyridazin-3-one 2 and with ethylenediamine, the pyrrolo[1,2-a]imidazole 3 was formed. Reaction of compound 1 and 2-aminoethanol yielded the pyrrolo[2,1-b]oxazolidinone 4 and the reaction with 3-aminopropan-1-ol resulted in the pyrrolo[2,1-b][1,3]oxazinone 5. With o-aminothiophenol tricyclic pyrrolo[2,1-b]benzothiazolone 6 was prepared. In comparison with 4–6, the structure of the new tri- and tetra-cyclic compounds 7–14 are discussed. With the starting oxoacid 1, the cyclic and bicyclic aminoalcohols gave the following fused heterocycles: cis- and trans-2-(hydroxymethyl)cyclohexane- and cyclohex-4-ene-amines yielded pyrrolo[1,2-a][3,1]benzoxazinones 7–10, diexo-3-(hydroxymethyl)bicyclo[2.2.1]heptane-2-amine and hept-5-ene-2-amine yielded the diexo (11 and 12) and diendo (13 and 14) methylene-bridged pyrrolo[1,2-a][3,1]benzoxazinones. The structures of the compounds were proved by 1D ¹H and ¹³C NMR spectroscopy, NOE difference spectroscopy and several different homo- and hetero-nuclear multipulse techniques (COSY, NOESY, HETCOR). The 1D ¹H NMR spectra were analysed by iterative spin-simulation using PERCH-software. Many interesting long-range couplings were found. Some aid for structural elucidation was gained from molecular modelling calculations. The crystal structures of 7, 9–11, 13 and 14 elucidated from the X-ray diffraction measurements do not differ significantly from the solution structures.