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Conformational Analysis. 30-A 1H and 13C NMR Stereochemical Study on N–Methyl–Substituted cis– and trans–Fused Octahydro–2H–1,3– and –3,1–benzoxazines

✍ Scribed by Kalevi Pihlaja; Jorma Mattinen; Ferenc Fülöp

Publisher
John Wiley and Sons
Year
1996
Tongue
English
Weight
369 KB
Volume
34
Category
Article
ISSN
0749-1581

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✦ Synopsis

The 'H and "C NMR spectra of cis-and trans-fused N-methyloctahydro-2H-1,3-and -3,l-benzoxazines and their 2-methyl derivatives were analysed. All trans-fused derivatives studied existed in biased double chair conformations with roughly equal contributions of the equatorial and axial N-methyl groups. Of the cis-fused isomers, both N-methyl-octahydro-2H-l,3-benzoxazine and its 2-methyl derivative attain exclusively the O i n conformation, whereas N-methyloctahydro-2H-3,l-benzoxazine is not conformationally homogeneous but a ca. 3 : 1 mixture of the N-in and N-out forms at 198 K and a 7:3 mixture at ambient temperature. Similarly, the 2-methyl derivative of N-methyloctahydro-2H-3,l-benzoxazine was found to be a cu. 3:2 mixture of C-2 epimers with the N-in and N-out conformations, respectively.

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