Long-range correlations ((n)j (C,H) n > 3) in the HMBC spectra of 3-(4-oxo-4H-chromen-3-YL)-acrylic acid ethyl esters

A systematic study about the long-range correlations observed in the HMBC spectra of a series of cis and trans 3-(4-oxo-4H-chromen-3-yl)-acrylic acid ethyl esters, and 5-hydroxy derivatives, was carried out. The results were compared with those observed in IMPEACH-MBC and CIGARHMBC spectra. An uncommon (5)J(C,H) between the methyl protons and the C-alpha to the carbonyl group was observed in these systems as well as in ethyl chrotonate. The complete assignments of the H-1 and C-13 NMR spectra are provided