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
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").
Booth, Harold,Dixon, J. Mark,Khedhair, Khedhair A.,Readshaw, Simon A.