Structural studies on abscisic-acid-synthesis intermediates: (1) 5,6-dihydro-4-methyl-6-(7,9,9-trimethyl-1,4-dioxaspiro[4.5]dec-7-en-8-yl)-2H-pyran-2-one and (2) 5,6-dihydro-4-methyl-6-(2',2',6'-trimethylspiro[1,3-dioxolane-2,4-[7]oxabicyclo[4.1.0]hept]-1'-yl)-2H-pyran-2-one |