Reactions of diaryl thioketones with diazomethane at room temperature afford 4,4,5,5‐tetraaryl‐1,3‐dithiolanes; the scope of this surprising 2:1 interaction has been studied for decades (Schönberg Reaction). The clue to the mechanism was our observation that the stoichiometry is 1:1 at −78 °C, and 2,5‐dihydro‐2,2‐diaryl‐1,3,4‐thiadiazoles are formed as primary [2+3] cycloadducts. They lose N2 at −45 °C in first‐order reactions generating diaryl thioketone S‐methylides which can be intercepted by thioketones (→1,3‐dithiolanes), multiple CC bonds, or acids HX. In the absence of trapping reagents, the elusive intermediates either dimerize furnishing 2,2,3,3‐tetraaryl‐1,4‐dithianes or give rise to 2,2‐diarylthiiranes by electrocyclization. Beyond thiobenzophenone and diazomethane, our main model reaction, the studies involve fluorene‐9‐thione, 4,4‐dimethoxy‐ and 4,4‐dichlorothiobenzophenone. The ring of 2,5‐dihydro‐2,2‐diphenyl‐1,3,4‐thiadiazole (8) is opened by LDA at −78 °C and derivatives of anion 12 are obtained. − In summa: The Schönberg reaction consists of two 1,3‐dipolar cycloadditions, linked by a 1,3‐dipolar cycloreversion.