The formation of cage phosphoranes and their rearrangements in the reactions of substituted 2-(3-oxo-3-phenyl)ethoxybenzo[: D] -1,3,2-dioxaphospholes with perfluorodiacetyl

The Kukhtin-Ramirez reaction of 2-(3-oxo-3-phenyl)ethoxy-benzo[d]-1,3,2-dioxaphospholes with perfluorodiacetyl was monitored by NMR methods. To our surprise the initial stage involved a kinetically controlled [4+4]-cycloaddition with the formation of a cage phosphorane containing a 2',5',8',9'-tetraoxa-2λ5-phosphaspiro[benzo[d][1,3,2]dioxaphosphole-2,1'-bicyclo[4.2.1]nonan]-3'-ene (compound 5) scaffold. Intermediate 5 then converts to spirophosphorane-4',5'-bis(trifluoromethyl)-2λ5-spiro[benzo[d] [1,3,2]dioxaphosphole-2-yl-2,2'-[1,3,2] dioxaphosphole (compound 4). Compound 4 further rearranges into a cage phosphorane derivative containing a [2,5]epoxybenzo[d][1,3,6,2]trioxaphosphocine] (compound 3) backbone.