STEREOCHEMICAL STUDIES 83. SATURATED HETEROCYCLES 76. PREPARATION AND CONFORMATIONAL STUDY OF PARTIALLY SATURATED 3,1-BENZOXAZINES, 3,1-BENZOXAZIN-2-ONES AND 3,1-BENZOXAZINE-2-THIONES

Article abstract of DOI:10.1016/S0040-4020(01)96537-8

The cis- and trans-2-amino-4-cyclohexene-1-carboxylic acids 1 and 3 react with imidates to give the condensed-skeleton, bicyclic cis- and trans-pyrimidin-4-ones 8 and 9.The amino acids 1 and 3 were reduced to the cis- and trans-1,3-aminoalcohols 6 and 7, which were cyclized by means of imidates to the bicyclic tetrahydro-4H-3,1-benzoxazines 10 and 11, or were converted, via the corresponding carbamates 14 and 15 into the tetrahydro-4H-3,1-benzoxazin-2(1H)-ones 16 and 17.The 2-thioxo analogues 18 and 19 were prepared by cyclization of the dithiocarbamates obtained from the aminoalcohols 6 and 7 by treatment with carbon disulphide.The trans-aminoalcohol 7 and its saturated analogue reacted with p-chlorobenzaldehyde to furnish the hexahydro 13 and octahydro-4H-3,1-benzoxazine 13a, respectively. 1H and 13C NMR studies showed that, similarly to the earlier-investigated analogues containing oxygen or unsubstituted nitrogen at position 1, the synthesized cis isomers 8, 10, 16 and 18 occurred as the preferred conformer in the heterocyclic twist inverse form of N-inside type (quasiaxal C6-N bond) (B).In the trans isomers containing a saturated C-2 atom (13 and 13a), H-2 and H-6 are in cis relative positions.