Unusual Ring‐Closure Reactions During the Oxidation of 1,1′‐Bi(3‐methylphosphol‐2‐ene) with Hexafluoroacetone — Formation of a Tricyclic Fluorine‐Containing Phosphorane

Reduction of the isoprene—PCl 3 adduct 1 with magnesium powder, or with Si 2 Cl 6 , furnished P ‐chloro‐3‐methyl‐phosphol‐2‐ene, 2 , in satisfactory yield. Further reduction of 2 with Si 2 Cl 6 gave the new trichlorosilyl‐3‐methylphosphol‐2‐ene, 3 . The reaction of 2 with magnesium powder, with 3 , or with 1/2 equivalent of Si 2 Cl 6 provided the new γ 3 P‐γP‐diphosphane 1,1′‐bi(3‐methylphosphol‐2‐ene) 4 . Reduction of 4 with Si 2 Cl 6 led to 3 . Oxidation of 4 with selenium gave the 1,2‐diphosphane diselenide, 5 . The oxidation of 4 with hexafluoroacetone led to a mixture of products, from which a novel tricyclic phosphorane 6 was separated. the structure of 196 was determined by X‐ray diffraction; the coordination geometry at phosphorus in distorted trigonal bipyramidal, with a very long equatorial P—C(CF 3 ) 2 bond of 193.2(2) pm.