Transition metal-catalyzed intramolecular [4+2] cycloadditions: Mechanistic and synthetic investigations

Article abstract of DOI:10.1016/S0040-4020(97)10223-X

The nickel-catalyzed intramolecular cycloaddition of dienes with unactivatable alkynes is found to proceed under mild conditions while the corresponding Diels-Alder cycloaddition of the same substrates either fails of occurs only under forcing conditions. The nickel-catalyzed cycloaddition is also shown to occur with retention of stereochemistry and is not significantly influenced by electronic effects. Finally, the catalyzed process is shown to be applicable to the synthesis of angularly substituted bicycles, including the CD ring systems of steroids and vitamin D.