1H–1H long range couplings in fused cyclopropanes. NMR spectral assignment and conformation of 17,18-cyclosteroids
Abstract
1 H–1H NMR couplings through four bonds (4JH–H) involving cyclopropane hydrogen were calculated for model compounds by semiempirical methods and used for the 13C and 1H NMR spectral assignment of 17,18-cyclosteroids. The couplings (4JHH) between cyclopropyl and non-cyclopropyl hydrogen follow an angular dependence which resembles that of allylic couplings. Solution conformations of rings C-D and the side-chain of 17,18-cyclopregnanes were determined from semiempirical molecular orbital calculations, three and four bond 1H–1H coupling constants and NOE measurements.