1,1-Dihalo-1-alkenes are important synthetic intermediates, which provide convenient and versatile routes to polysubstituted alkenes and carbo- or hetero-cycles. In this paper, the preparations of 1,1- dihalo-1-alkenes were reviewed first. Secondly, the applications of 1, 1-dihalo-1-alkenes in organic synthesis were discussed in detail: (1) the reaction of 1,1- dibromo-1-alkenes with metal or metal reagents forms alkylidene carbenes via- α -elimination, which was followed by the common reactions of carbenes, such as 1,2-migration or 1,5-C－H insertion, etc. Metal species involved can be magnesium, organolithium, SmI2, stannyl anion and palladium; (2) the formation of 1-alkynyl bromides or alkynes via the elimination reaction; (3) regioselective H-abstraction-radical cyclization reaction; (4) inter- and intramolecular cross-coupling reactions, reductive hydrolysis, and formal oxidative homologation under the catalysis of palladium. Recently, we have developed the bicyclic carbopalladation reaction, which affords the fused bicycles with different patterns in just one "shot", such as 5,6-, 6,6-, 6,7-, and 7,7-bicycles. Possible mechanisms of these reactions were also discussed.

Key words: ELIMINATION REACTION, INTERNAL MOLECULAR REACTION, COUPLED, ORGANIC SYNTHESIS, ALKENE P, HALOHYDROCARBON P