Conformational analysis. XXVII—A ¹H and ¹³C NMR conformational study of cis‐ and trans‐annelated 2‐p‐nitrophenyl‐4,5‐ and ‐5,6‐tetramethyleneper‐hydro‐ and 2‐p‐chlorophenyl‐4,5‐ and ‐5,6‐tetramethylenedihydro‐1,3‐oxazines

Abstract

The 400 MHz 'H NMR spectra of cis-and trans-annelated Z-p-nitropheny1-4,S-and -5,6-tetramethyleneperhydro-and Z-p-chlorophenyl-4,S-and -5,6-tetramethylenedihydro-1,3-oxazines were recorded. The AMKX subspectra due to the protons at C-4, C-5 and C-6 were analysed.

Modeling NMR Parameters by DFT Methods as an Aid to the Conformational Analysis of cis-Fused 7a(8a)-Methyl Octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

“…The systematic study of the structure and stereochemistry of such ring-saturated heterocyclic compounds has been undertaken for many years concomitant with improvements to their synthetic methodologies 19 and, in addition to being inherently interesting, many heterocyclic compounds also display marked physiological activity which provides further impetus for their study. Similar compounds possessing, or lacking, the 7a/8a-methyl have been studied earlier [20][21][22][23][24][25][26][27] whereby it was ascertained that the cis-fused ring system in 3,1-oxazine (1,3-oxazine) derivatives can attain either a biased N-in or N-out (O-in or O-out) conformation (see Scheme 1), or exist as an interconverting equilibrium mixture of the two conformers depending on their relative stabilities as determined by the ring size, the ring substituents, and the ring structure. The compounds of this set displayed a mix of different dynamics under the current NMR conditions, 18 ranging from totally biased systems, to simple interconverting pairs that are able to be spectroscopically frozen, to complex systems beyond dissemination.…”