The Diels-Alder reaction was conducted in refluxing xylene. After 4 and 6h, respectively, the mixture of diastercomeric cycloadducts 821/92 and Sb/9b were isolated in 96" 4, and 99% yield. The r-is/trans ratio was determined from “C-NMR spectra of the reaction mixtures. The unsubstituted 7a gave trans-annulated 9a preferably (ni-d<: 12: 38%). whereas the reaction of the methyl derivative 7b was cis-selective (nide= 67%). The diastereomers 8 and 9 ...
![4-[2-(3-methylbut-2-enoxy)phenyl]-2-oxobut-3-enoic acid Structure](https://image.chemsrc.com/caspic/169/112881-83-1.png)