Studies on organophosphorus compounds—XXXVII: Syntheses of δ5-1,2,3-diazaphospholines and indoles from hydrazones

2,4-Bis(4-methoxyphenyl-1,3,2,4-dithiadiphosphetane-2,4-disulfide, 1, reacts with phenylhydrazones of methylketones to give Δ⁵-1,2,3-diazaphospholines, 3; in one case 2-methyl-3-phenylindole, 4, was also isolated. Phenylhydrazones of cyclopentanone and cyclohexanone similarly yield the corresponding annulated P-heterocycles, 6a, 6b and as by-products the indoles 7a and 7b, respectively. The sole product from the reaction of 1 with the phenylhydrazone of 1,3-diphenyl-2-propanone is 2-benzyl-3-phenylindole, 9. A mechanism for the formation of the diazaphospholines is suggested.