Octahydro-2/7-1 ,3-benzoxazines conformations

A careful analysis of the H and - C NMR spectral parameters (H,H coupling constants and shielding effects) established that the predominant conformation of the hetero ring for diexo-d ca- and d/ejco-l,2,3,4,4a,5,8,8a-octahydro-5,8-methano-3,l-benzoxazines is the endo-ho i 339A, whereas that for the corresponding diendo derivatives is the exo-boat 339B (85T5159). 

Of the four diastereomeric 8,9,10,11,1 la,1 lb,12,13-octahydro-7a//-quino-[l,2-c][l,3]benzoxazines (304), three prefer the trans-fused conformations 305-307. The overlap of the nitrogen lone-pair orbital with the aromatic ring affects the Jgem and Aae values of the NCH20 protons in these isomers (Sections II,B,1 and 2), and the Bohlmann absorption (Section II,E,1) is no... 

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