Diastereoselective synthesis of functionalised carbazoles via a sequential Diels-Alder/ene reaction strategy

An operationally simple one-pot, three-component, diastereoselective synthesis of saturated carbazoles and related pyridazino[3,4-b] indoles, based on two sequential intermolecular pericyclic reactions, is described. The reaction sequence involves an intermolecular Diels-Alder (D-A) reaction of a 3-vinyl-1H-indole, containing an electron withdrawing N-protecting group, with a suitable dienophile. Due to the electron withdrawing nature of the N-protecting group the resultant D-A cycloadducts are sufficiently stabilised to allow for a subsequent in situ diastereospecific intermolecular ene reaction to take place with an added enophile, generating functionalised carbazoles with relative stereocontrol of up to four stereocentres.