Unusual In‐Situ Preorganization and Postoxidation Steps Observed in Diels‐Alder Reactions of Styrylcyclohexene Dienes

Abstract Unusual products were obtained from cycloadditions reactions of two series of styrylcyclohexene dienes with dienophiles maleic anhydride and N ‐phenylmaleimide. Experimental studies revealed that various dienes 3 underwent an initial in‐situ dehydration/double bond rearrangement prior to cycloaddition with maleic anhydride to give products 5 in 78–88 % yields. Alternatively, the cycloadducts of the reactions of 4 with N ‐phenylmaleimide were hydoxylated stereoselectively in the same pot to give products 7 , along with the usual adducts 6 in 83–89 % yields. Further, the reactions of the diene 4 with the dienophile dimethyl acetylenedicarboxylate were also studied, leading to the formation of the respective adducts 10 in 72–81 % yields. The stereochemistry of the new products was assigned based on their spectroscopic data and, in some cases, with X‐ray crystallography experiments.