Stereochemical studies. Part 78. Saturated heterocycles. Part 65. Synthesis and spectroscopic studies of cis-5,6-trimethylene-, and cis- and trans-5,6-tetra-and -pentamethylene-1,3-oxazinan-4-ones

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Abstract
N-Methyl-cis-5,6-trimethylene-, and cis- and trans-5,6-tetra- and -pentamethylene-1,3-oxazinan-4-one derivatives (15) and (16) were prepared by cyclisation, with aldehydes, of the appropriate alicyclic 2-hydroxy-1;-carboxamides. In each case, formation of the new C-2 centre of chirality was found to take place stereospecifically and only the (r-5,t-2,t-6) and (r-5,c-2,c-6) diastereoisomers, respectively, were formed. The conformations of the N-methyl-and N-unsubstituted cis-trimethylene-, cis-tetramethylene-, and cis-pentamethylene-1,3-oxazinan-4-ones (13)–(16) were determined by 1H and 13C n.m.r. spectroscopy in solution. Good agreement was obtained with the earlier data established by X-ray diffraction analysis of the crystalline substances. The relative steric structure of the C-2 centre of chirality was also proved by d.n.O.e. measurements. It was found that the substituent at position 2 did not affect the conformation significantly.

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