STEREOCHEMICAL STUDIES-54 SATURATED HETEROCYCLES-35

Article abstract of DOI:10.1016/S0040-4020(01)88695-6

cis and trans-5,6-Trimethylene-3,4,5,6-tetrahydro-1,3-oxazin-2-ones and thiones (11-20) were synthesized from cis and trans-2-aminomethylcyclopentanols (6-10) by reaction with urea, ethyl chloroformate, carbon disulphide, or thiophosgene.The cyclization reactions were also successful with the trans-amino-alcohols, at variance with earlier literature data relating to 1,2-disubstituted 1,3-bifunctional trans-cyclopentane derivatives.X-ray diffraction analysis of trans-5,6-trimethylene-3,4,5,6-tetrahydro-1,3-oxazine-2-thione (17) shows that the exocyclic C<*>S sp² bond takes part in a co-planar delocalized p?-p? bond system formed on the S(10), O(1), N(3) and C(2) atoms, and consequently both the C(2)-N(3) <1.304(7) Angstroem> and C(2)-O(1) <1.337(7) Angstroem> bonds gain some multiple bond character.The endocyclic bond angles at C(2) and N(3) are significantly opened, compared with those in related heterocycles.Of the bonds in the six-membered hetero ring, C(5)-C(6) is significantly shortened <1.448(9) Angstroem>.The remarkable ring closure reaction of the trans cyclopentane derivatives can be explained by the above findings. ¹H NMR data on compounds 11-20 suggest conformationally homogeneous systems and the predominance of the O-inside conformers of the cis isomers.