Unexpected Thermal Reactivity of Phosphirano[1,2]thiaphosphole P–WCO5Complexes

Spiro[fluorene9,6′[2]thia[1]phosphabicyclo[3.1.0]hex[3]enes] 7a–chave been obtained in one step from 3,5diaryl1,2thiaphospholes and 9diazofluorene or its 2,7dibromo derivative. The bicyclic phosphiranes are stable against water and resist attempts at sulfuration or selenation of the phosphorus atom. However, cleavage of the P–C ring fusion with hydrogen chloride followed by hydrolysis led to the monocyclic 29Hfluoren9yl2,3dihydro1,2thiaphosphole 2oxides 8a–c. Phosphiranes 7a–calso react to form the hexacarbonyltungstenP–W complexes 10a–creadily and in high yields. These complexes rearrange in toluene solution at 50–80 °C to form the spiro[fluorene9,2′[1]phospha[6]thiabicyclo[3.1.0]hex3ene]WCO5P–W complexes 11a–c, which are the first representatives of ringfused thiaphosphiranes. Compound 11ais readily desulfurated with tributylphosphane to form the highly oxygensensitive spiro[fluorene9,2′[2H]phosphole] 13, which is reconverted into 11aupon treatment with sulfur. Bicyclic 1,3,2dithiaphospholanes 12a–care formed as minor byproducts of the thermal isomerization of phosphiranes 10. Compound 10aslowly rearranges in solution to give 12aas the sole product. Compounds 12may result from a formal [3+2] cycloaddition reaction of an α,βunsaturated thione, formed by partial decomposition of 10, with a dipolar valence isomer of 10or 11, featuring aWCO5complexed thiocarbonylphosphaylide dipole R2C=S+–P–R. WCO5complexation is not a prerequisite for the cycloaddition reaction: the uncomplexed phosphiranothiaphosphole 7areacts with thiobenzophenone in the same way to form the bicyclic 1,3,2dithiaphospholane 18in high yield. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009