The title compound (DMBU) is a useful diene in [4+ 21 cycloadditions. Since DMBU is readily obtained in two steps from 1, 4-dihydroxy-2-butyne, it should be regarded as an inexpensive and abundant starting material. Diels-Alder products were obtained from DMBU and the dienophiles, dimethyl acetylenedicarboxylate, ethyl propiolate, benzyne, fumaronitrile, tetracyanoethene, maleic anhydride, 1, 2-dibenzoylethene, diethyl ...