2-Butenoicacid, 2-methyl-,7,8-dihydro-8,8-dimethyl-6-[(3-methyl-1-oxo-2-butenyl)oxy]-2-oxo-2H,6H-benzo[1,2-b:5,4-b']dipyran-7-ylester, [6R-[6a,7b(Z)]]-