Effects of N-substitution on the fragmentations of some cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and related thiazines

Abstract

Six cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and four related thiazines were prepared and their mass spectrometric behavior was studied by means of metastable ion analysis and exact mass measurement. In most of the fragmentations, extensive rearrangements took place. The decompositions through the retro-Diels-Alder reaction initiated by the double bond dominated in the case of the unsubstituted compounds. The effect of the double bond, however, was greatly outweighed by the effect of the substituent on the ring nitrogen atom. In comparison with the unsubstituted compounds, both electron-releasing (methyl) and electron-withdrawing (benzyl) substituents increased the contribution of the ring cleavage reactions in the heterocyclic part of the molecule; in the case of the benzyl group the loss of the substituent also became important. For isomeric compounds, the relative peak intensities were so different that such compounds were easy to differentiate.

Flash Vacuum Pyrolysis (FVP) of cis‐N‐phenyl‐hexahydro‐2H‐benzo[d][1,3]oxazin‐2‐imine and Thiazin‐2‐imine Derivatives

“…Compound 1 a was prepared through the methodology that we have recently described, [20] while compounds 1 b – c and 2 a – c were prepared by two different ways, modifying the original procedure from a previous publication [32] . Moreover, the synthesis of starting materials, which are the amino acid 8 and amino ester 9 , was performed as it was described for the synthesis of hexahydroquinazolin‐4(1H)‐ones [17] .…”

“…The only available approximation was the article published some time ago showing the deep analysis of 1,3‐oxazines and 1,3‐thiazines fragmentation through MS. There, it was established that cleavage could take place via radical intermediates or in a concerted way [32] . To this date, no previous reports exist about the fragmentation mechanisms of N ‐phenyl‐hexahydro‐2 H ‐benzo[ d ][1,3]oxa(thia)zin‐2‐imines.…”

“…As it was stated above, compounds 1 a – c and 2 a – c were prepared by two different ways, modifying the original procedure published some time ago, [32] while the amino acid 8 and amino ester 9 , were prepared as it was described for the synthesis of hexahydroquinazolin‐4(1H)‐ones [17] . All chemical and physical properties of prepared compounds were similar to those reported by Fülöp et al ., [19] Vainiotalo et al [32] . and Peláez et al [17] …”

ChemInform Abstract: Fused‐Skeleton Saturated Six‐Membered 1,3‐N,O, N,N and N,S Heterocycles. Fused‐Skeleton Aryl‐Substituted Saturated Isoindolones

“…When the corresponding aminoalcohols are applied instead of the haloalkylamines, 2-thioxoquinazolin-Cones (166)(167)(168)(169) are formed. The ring closure of (1 66-1 69) takes place in boiling ethanol containing 22% HCI, resulting in the tricyclic thiazolo-or phosgene with 3 equivalents of sodium hydrogenthiazino[2,3-b]quinazoline derivatives (1 50-1 53).…”

Stereochemical effects in the EI mass spectra of cis- and trans-fused hexahydro-3,l-benzoxazines and –benzothiazines

“…As a continuation of our systematic mass spectrometric studies on 1,3-and 3,1-octahydrobenz-oxazines and related thiazines [2][3][4][5][6][7][8] the mass spectrometric behavior of cis-/ transfused isomeric pairs shown in Scheme 1 is now studied.…”