Download PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... The synthesis of two new heterodienes and their regioselective [4+2]cycloaddition reactions with several bromo-naphthoquinones allowed us to prepare the first angucyclinone and angucycline 5-aza-analogues. ... The push–pull dienes (EE)-1a and (EE)-1b, required for our study, ...