The hetero-Diels-Alder reaction is one of the most powerful transformations in
the chemistry toolbox for the synthesis of heterocycles. In this article, the recent developments
of this reaction are presented involving heterodienophiles such as imines, azenes, carbonyls,
thiocarbonyls, and nitroso compounds as well as heterobutadienes such as azabutadienes,
diaazabutadienes, oxabutadienes, thiabutadienes, nitrosoalkenes, and nitroalkenes.