Stereochemistry of alkyl 3‐substituted 4‐halotetrahydro‐2‐oxo‐3‐furancarboxylates: 2 — 1 H and 13 C NMR spectra

The 1 H NMR parameters of methyl 3‐substituted cis ‐4‐halotetrahydro‐2‐oxo‐3‐furancarboxylates are reported, with assignments of the ring protons based on solvent‐induced changes in the vicinal trans coupling constants, 3 J (H‐4, H‐5). Preferred conformations, ce with a pseudo‐equatorial halogen for the cis isomers and ta with a pseudo‐axial halogen for the trans isomers, have been suggested on comparison of the magnitudes of J(trans) and J(gem) in both series. The 3 J ( 13 CH 3 , H‐4) values measured for methyl cis ‐4‐bromotetrahydro‐3‐methyl‐3‐furancarboxylate, methyl trans ‐4‐bromotetrahydro‐3‐methyl‐3‐furancarboxylate and trans ‐3,4‐dibromodihydro‐3‐methyl‐2(3 H )‐furanone have confirmed the stereochemical assignments.