According to anti?Bredt rule,if olefin strain (OS) of alkene with double bond in bridgehead is less than 71 kJ/mol,it can be isolated at room temperature.The OS of bicyclo[4.2.1]?1(8)?nonylene is less than 71 kJ/mol,conforming with anti?Bredt rule.A novel synthetic route of gram?scalable bicyclo[4.2.1]?1(8)?nonylene was reported,which was synthesized in seven steps with 17% overall yield,characterized by starting from 2?cycloheptenone using a vinyl magnesium bromide?mediated 1,4?conjugation as addition and an intramolecular Wittig reaction as the key steps.Different from the previous synthesis,the raw materials used in this method are all commercially available,which avoids the synthesis of raw materials themselves and simplifies the synthesis route.In addition,intramolecular Wittig reaction is used as the key reaction to avoid the generation of isomers.It is very challenging to synthesize alkene with double bond in bridgehead because of their high strain energy and instability.However, development of synthetic routes for such compounds is of great significance for further study of their chemical properties and application.