Given the task definition and input, reply with output. In this task, you will be given a passage to read. A fill in the blank question will be given to you.  Your answer should fit the blank appropriately.

 The original publication by Johnson concerned the reaction of 9 @-@ dimethylsulfonium fluorenylide with substituted benzaldehyde derivatives . The attempted Wittig @-@ like reaction failed and a benzalfluorene oxide was obtained instead , noting that  Reaction between the sulfur ylid and benzaldehydes did not afford benzalfluorenes as had the phosphorus and arsenic ylids .  The subsequent development of ( dimethyloxosulfaniumyl ) methanide , ( CH3 ) 2SOCH2 and ( dimethylsulfaniumyl ) methanide , ( CH3 ) 2SCH2 ( known as Corey – Chaykovsky reagents ) by Corey and Chaykovsky as efficient methylene @-@ transfer reagents established the reaction as a part of the organic canon . fill in the blank  :  The original publication by Johnson concerned the reaction of 9 @-@ __________________ fluorenylide with substituted benzaldehyde derivatives . 

 dimethylsulfonium 