M Saeed Abaee, Zahra Shabani, Mohammad M Mojtahedi
A DBU/H2O medium was used to explore the reaction of isophorone 1 with aromatic aldehydes at room temperature. The reaction gave adducts 3via selective substitution at the exocyclic methyl position γ to the C[double bond, length as m-dash]O group of 1, as opposed to reacting with one of the two available active endocyclic methylenic sites. A slight temperature increase in the same mixture produced the respective diene 4. Stepwise treatment of 4 with dimethyl fumarate in refluxing toluene gave a mixture of the two possible endo Diels-Alder adducts 5 and 5' in an approximately 5 : 1 ratio, through a highly stereospecific endo pathway, while addition of SnCl4 to the same mixture solely produced 5. Alternatively, one-pot combination of 1, the aldehydes, and the dienophile gave a 19 : 1 mixture of 5 and 5' within 2 h treatment of the reactants in DBU/H2O mixture. NMR analysis and X-ray crystallography of the adducts confirmed the proposed structures for 5 and 5'.