Synthesis and reactions of the versatile synthetic block bicyclopropylidine and its derivatives are introduced. Bicyclopropylidene can be prepared in practical scale starting from methyl cyclopropanecarboxylate. Monosubstituted derivatives are easily accessible by deprotonation-electrophilic substitution reactions. Reactivity of the highly strained bicyclopropylidene possesses the following characterics : (1) enhanced kinetic acidity as manifested by the facile deprotonation of the four methylene groups; (2) enhanced reactivity of the C= C bond; (3) C-C bond adjacent or opposite to the central C== C bond can be cleaved; (4) possible combination of these reactivities. Several typical reactions of bicyclopropylidene derivatives are described which include [2 + rc] cycloaddition reactions with the central C= C bond, electrophilic and radical reactions, 1,3-dipolar cycloadditions and transition metal catalyzed reactions.

Key words: bicyclopropylidene;ELECTROPHILIC REACTION;ADDITION REACTION, FREE RADICAL REACTION;CYCLOADDITION REACTION