Perfluorovinylsulfur pentafluoride

How does perfluorovinylsulfur pentafluoride react with 1,3-butadiene What products P and Q are formed ... 

As in Explanation 89, these two compounds do not react in the sense of the Diels-Alder reaction. Instead, a cyclobutane derivative is formed by cycloaddition. The reaction is a free-radical process starting with single electrons on carbons 1 and 2 of perfluorovinylsulfur pentafluoride. Carbon 1 of the 1,3-butadiene joins the difluoromethylene group of the perfluorovinylsulfur pentafluoride because in this way, the newly formed biradical can better accommodate the single electron on the carbon next to the SF5 group. The biradical closes the ring in such a way that two stereoisomers, P and Q, cis- and trans-2,3,3-trifluoro-l-vinyl-2-cyclobutyl-sulfur pentafluoride, are formed in equal amounts [122]. 

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