SYNTHESIS AND CLEAVAGE REACTIONS OF SOME DIBENZOPHOSPHOLE DERIVATIVES

Several heterocyclic phosphine oxides and phosphonium salts have been prepared and cleaved with sodium hydroxide. Cleavage of 5-benzyl-5-phenyldibenzophospholium chloride (III) and 5-benzyl-5-methyldibenzophospholium iodide (VI) gave 5-phenyldibenzophosphole 5-oxide (II) and 5-methyldibenzophosphole 5-oxide, respectively. In these cases, the cleavage of the benzyl group appears to proceed from a position not colinear with the phosphorus-oxygen bond in the trigonal-bipyramidal intermediate. Cleavage of 5-phenyldibenzophosphole 5-oxide (II) and 5-benzyldibenzophosphole 5-oxide (V) led to exclusive ring opening for II and preferential ring opening for V. The unexpected instability of the heterocyclic ring in V suggests that this cleavage reaction does not proceed via a trigonal-bipyramidal intermediate but through a mechanism similar to that of an Sn2 reaction. © 1969, American Chemical Society. All rights reserved.