F Cyclobutene

In a reaction similar to 7-47, certain sulfones, both cyclic and acylic,461 extrude S02 on heating or photolysis to give ring-contracted products.462 An example is the preparation of naphtho(f )cyclobutene shown above.463 In a different kind of reaction, five-membered cyclic sulfones can be converted to cyclobutenes by treatment with butyllithium followed by LiAIH4,464 e.g.,... 

With CF3C=CCF3 or olefins with an internal double bond such as cis- or fraras-F-2-pentene, F-cyclobutene, or l,2-dichloro-l,2-difluoro-ethylene, or with a geminally disubstituted olefin such as 1,1-dichloro-2,2-difluoroethylene, only fully fluorinated products were obtained, likely through a nucleophilic fluorination mechanism. This fact, plus the necessity for a Lewis acid catalyst for addition to proceed, is evidence for an electrophilic addition mechanism. Others have suggested polar addition of BF3 to the olefin with RfBF2 as a reactive intermediate (294). 

The olefin F-cyclobutene, which would be derived from the parent compound by loss of F2, definitely is not produced. A standard sample of F-cyclobutene eluted between the peaks identified as Cr,Fi2 and C0Fi4, where no radiolysis product appeared. Since the parent F-cyclobutane tailed badly on the silica gel column used, the presence of other possible C4 fluorocarbons such as n-C4F8 or n-C4Fi0 could have been masked. 

Dithiocin 111 was isolated in low yield along with other products in the reaction of 1,2-dichloro-F-cyclobutene with BuLi and sulfur chlorides. ... 

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