Chlorination of 2,2,2,5-tetrachloro-6-methylbenzo[d]-1,3,2-dioxaphosphole

An NMR investigation has shown that the reaction of 2,2,2,5-tetrachloro-6-methylbenzo[d]-1,3,2-dioxaphosphole 2 with an excess of molecular chlorine occurs stepwise with high stereoselectivity to give 2,3,4,5,6,6-hexachloro-3-dichlorophosphoryl-5-methylcyclohex-1-ene 4, which then undergoes stabilization via a 3,3-sigmatropic shift of the dichlorophosphonate fragment to give 1,2,4,4,5,6-hexachloro-3-dichlorophosphoryl-5-methylcyclohex-1-ene 5. The configuration of the hydrolysis product of the latter (1,2,4,4,5,6-hexachloro-5-methyl-3-phosphorylcyclohex-1-ene 6) was established by single crystal X-ray diffraction.