Tetrafluorobenzyne reacts with 6-methoxytetralin and with 3,17β-dimethoxyoestra-1 (10),2,4-triene to give 1,4-cycloadducts. The adducts without a bridgehead methoxy-group are readily hydrolysed to the ketones, and the photolyses and pyrolyses of these ketones are briefly discussed. Benzyne and tetrachlorobenzyne react with 3β,6β-diacetoxy-5-methyl-19-nor-5β-cholesta-1(10),9(11)diene to give 1,4-cycloadducts.