Organophosphorus Compounds; 52.¹ Phosphatriafulvenes and Their Reactions with Electrophiles

Electrophilic reagents attack the phosphatriafulvenes 1a and 1b exclusively at the phosphorus atom. Hence 1b is methylated by methyl iodide to furnish the cyclopropenylium iodide 3 which, in turn, is converted to the triazine 6 by reaction with sodium azide. Ketenes 8 react with 1a through subsequent P → O silyl shifts to give the vinylphosphatriafulvenes 10. Isocyanates 13a and 13b behave analogously (→ 15). In the reactions of 1a with isothiocyanates 13c and 13d, in contrast, a P → N silyl shift is observed which leads to the formation of 16. Acetylenedicarboxylates 17 undergo insertion into the P/Si bond of the silylated phosphatriafulvene 1a (→ 19). In the case of the reaction of the mesitylsubstituted phosphatriafulvene 1b with 17, kinetically controlled formation of the dihydrooxophosphinines 20 takes place; at room temperature, the latter products undergo slow rearrangement to give the thermodynamically more stable isomers 21.