Experimental studies of the anomeric effect. Part III. Rotameric preferences about the exo-cyclic c2-x bond in equatorial and axial 2-methoxy-and 2-methylamino-tetrahydropyrans

Article abstract of DOI:10.1016/S0040-4020(01)81971-2

Values of³ J(CC), ³J(CH), ⁴J(CH) and ³J(HH), supported by n.O.enhancements, in nmr spectra of 2-methoxy- and 2-methyl-amino-tetrahydropyrans, point to a very strong preference for rotamers in which an _exo-cyclic heteroatom lone pair is antiperiplanar to the _endo-cyclic C₂-O bond ("_endo-anomeric effect").