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1 H, 13 C, and 15 N NMR stereochemical study of cis ‐fused 7a(8a)‐methyl and 6‐phenyl octa(hexa)hydrocyclopenta[ d ][1,3]oxazines and [3,1]benzoxazines
Author(s) -
Tähtinen Petri,
Sinkkonen Jari,
Klika Karel D.,
Nieminen Ville,
STájer Géza,
Szakonyi Zsolt,
FüLöp Ferenc,
Pihlaja Kalevi
Publication year - 2002
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.10056
Subject(s) - chemistry , conformational isomerism , epimer , substituent , cyclopentane , stereochemistry , hexa , steric effects , methyl group , chirality (physics) , cyclohexane conformation , anomeric effect , anomer , crystallography , group (periodic table) , molecule , organic chemistry , hydrogen bond , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark
Four 7a‐methyl octa(or hexa)hydrocyclopenta[ d ][1,3]oxazines, five 8a‐methyl octa(or hexa)hydro[3,1]benzoxazines, two 6‐phenyl hexahydro[3,1]benzoxazinones, and 8a‐methyl hexahydro[1,3]benzoxazinone, all cis ‐fused, were prepared and their stereostructures studied by various one‐ and two‐dimensional 1 H, 13 C, and 15 N NMR spectroscopic methods. In solution, the cyclopentane‐fused 2‐oxo derivatives and the 1,3‐benzoxazinone were found to attain exclusively the N‐in / O‐in conformation, whereas the 6‐phenyl 2‐oxo/thioxo derivatives were found to be present predominantly in the N‐out conformation. The C‐2 unsubstituted and the 2‐oxo/thioxo 7a/8a‐methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N‐in and N‐out conformations. The C‐2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C‐2) with the N‐in conformer predominating for one epimer and the N‐out conformer predominating for the other, with both predominating conformers having the C‐2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2‐methyl derivatives with N‐out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C‐2 methyl being favored. Chirality 14:187–198, 2002. © 2002 Wiley‐Liss, Inc.