Diethyl chloromalonate (Diethyl α-chloromalonate) is a 2-halo-1,3-dicarbonyl compound. It participates in K2CO3-catalyzed domino reactions (Michael alkylation, Mannich alkylation, and aldol alkylation) of salicylic aldehyde derivatives to afford functionalized 2,3-dihydrobenzofurans. It reacts with Cs2CO3 in the presence of elemental S8 or Sen to afford the corresponding diethyl thioxo- or selenoxomalonates, which can be trapped in situ with various 1,3-dienes.