THE STABLE (PHOSPHINO)(SILYL)CARBENE AS A USEFUL BUILDING-BLOCK - SYNTHESIS AND REACTIVITY OF 2-PHOSPHORUS-SUBSTITUTED 2H-AZIRINES

(dicyclohexylamino)phosphino]trimethylsilylcarbene (1) reacts with ben zonitrile leading to the corresponding 2-phosphino-2H-azirine 3 in 85 % yield. Treatment of 3 with trifluoromethanesulfonic acid, methyl tri fluoromethanesulfonate, or elemental sulfur leads to the P-hydrogeno-2 -phosphonio-, P-methyl-2-phosphonio-, or 2-thioxophosphoranyl-2H-aziri ne (4, 5, and 7) in 77, 87, and 91% yields, respectively. Irradiation of 3 gives rise to the 1,2 lambda(5)-azaphosphete 8 (98% yield). Treat ment of 3 with BF3 . OEt2, BH3 . SMe2, Lawesson's reagent, or methyl i sothiocyanate gives heterocycles 9 (90% yield), 10 (76% yield), 12 (83 % yield), or 13 (80 % yield), while under the same experimental condi tions, heterocycle 8 reacts with the same reagents to give 9 (82% yiel d), 11 (83% yield), 12 (86% yield), and 15 (56% yield), respectively. Thermolysis of the P-hydrogeno-2-phosphonio-2H-azirine 4 at 55 degrees C leads to the cationic, four-membered heterocycle 17 (96% yield), wh ile photolysis of the P-methylazirine analogue 5 in the presence of di methyl acetylenedicarboxylate affords pyrrole 19 (64% yield). Irradiat ion of the thioxophosphoranyl azirine 7 gives the 1,3,5 lambda(5)-thia zaphosphole 20 in 79 % yield. The influence of the coordination state of phosphorus on the reactivity of 2-phosphorus-substituted 2H-azirine s is studied.