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The W(CO)5 and Fe(CO)4 complexes of the bicyclic phosphirane 3,5,6,6-tetraphenyl-1-phospha-2-thiabicyclo[3.1.0]hex-3-ene undergo a thermal 2-phenylphosphirane --> dihydrophosphaisoindole ring expansion, while the free phosphirane suffers both a [2 + 1] cycloreversion and a fragmentation yielding a butadienyl sulfide.

1,2-Thiaphospholes 3a,b react with (1-diazo-2-oxoalkyl)silanes 1a−c to form [1,2] ,2]thiaphosphole systems 4 with cis-anti-cis configuration of the tricyclic framework. They are accompanied by small amounts of compounds 5 that are presumably the cis-syn-cis isomers of 4, and 6-alkylidene-1-phospha-2-thiabicyclo[3.1.0]hex-3-enes 6. It is likely that these reactions proceed by [3+2] cycloaddition of diazocumulenes, which coexist with diazo compounds as minor equilibrium components, at the P=C bond of the heterophospholes, followed by N 2 elimination and formation of short-lived 2-alkylidene-

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enes] 7a-c have been obtained in one step from 3,5-diaryl-1,2-thiaphospholes and 9-diazofluorene or its 2,7-dibromo 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 2-(9H-fluoren-9-yl)-2,3-dihydro-1,2-thiaphosphole 2-oxides 8a-c. Phosphiranes 7a-c also react to form the hexacarbonyltungsten-(P-W) complexes 10a-c readily and in high yields. These complexes rearrange in toluene solution at 50-