Lactonization of N-Acyl-N-(2-cyclopent-1-en-1-yl-6-methylphenyl)glycines upon Raction with Halogens

A study was carried out to identify the influence of the size of the cycloalkenyl ring and the nature of the substituent at the nitrogen atom on the structure and stability of the halogen cyclization products N-acyl-N-(2-cyclopent-1-en-1-yl-6-methylphenyl)glycines, which were synthesized from N-acyl-2-(1-cyclopenten-1-yl)-6-methylanilines and methyl bromoacetate followed by alkaline hydrolysis of the resulting methyl glycinates. It was shown that in the reaction of N-benzoyl and N-(4-nitrobenzoyl) derivatives with molecular bromine, 2′-bromo-9-methyl-N-aroyl-1,2-dihydro-3H-spiro[4,1-benzoxazepine-5,1′-cyclopentan]-3-ones and 8-methyl-N-aroyl-3,3a,6,7- tetrahydrobenzo[e]cyclopenta[g][1,4]oxazocin-5(2H)-ones is formed, the ratio of which in the case of the N-benzoyl derivative is ≈1:4, in the case of the N-nitrobenzoyl analogue reaches ≈1:1. Spiro-fused benzoxazepinones, unlike eight-membered heterocycles, are unstable. Samples of these compounds isolated by chromatography decompose with strong darkening within a few hours. In the case of the N-acetyl homologue, the resulting halogenlactonization products cannot be isolated due to their rapid decomposition. The aS*,R*-configuration of the substituents along the N⁷–C⁷a axis and at C³a center of chirality of N-aroylbenzoxazocinones was established by X-ray diffraction studies.