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Phosphaalkynes 2 undergo cocyclooligomerization reactions with the phosphinidene 14 or the phosphinidene-W(C0)5 complex 18 to furnish the phosphorus-carbon cage compounds 16 or 23. The phosphinidene 14 is generated by the thermal reaction of 2a-c with the phosphole 11, a process in which the initially formed 7-phosphanorbornadienes 12a-c decompose to the h3-phosphinines 13a-c and the desired reactive intermediate. When three further equivalents of the phosphaalkynes 2a-c are employed, the tetraphosphahomoquadricyclanes 16a-c can be isolated in 53-65% yields. The second approach is based on the thermal fragmentation of 17 to generate the phosphinidene-W(CO), complex 18 which, in turn, reacts with four equivalents of the phosphaalkynes 2a or b to produce the pentaphosphadeltacyclanes 23a or b. The constitutions of these novel phosphorus-carbon cage compounds were confirmed by X-ray crystal structure analyses of 16a and 23a.

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Tropone (11, with its 8n-electron system, and the kinetically stabilized phosphaalkynes 3a-c undergo cycloaddition reactions, in dependence on the stoichiometry and reaction conditions, to furnish co-oligomeric phosphorus-carbon cage compounds 5a,b or 9a-c, respectively. When tropone (1) is subjected to thermolysis conditions in the presence of a n excess of the phosphaalkyne 3a o r b but in the absence of a solvent, the homo-Diels-Alder adducts Sa o r b are isolated in 21% or 23% yield, respectively. The peri-and regioselectivities observed for this two-step reaction sequence can be precisely defined on the basis of semiempirical MO calculations (frontier orbital theory, PM3). On the other hand, when tropone (1) is heated with equimolar amounts of the phosphaalkynes 3a-c in toluene, the pentacyclic compounds 9a-c are formed in 51-64% yields as subsequent products of the [8 + 21 cycloaddition of tropone with the tetracyclic species 5a-c.Diels-Alder or, respectively, 1 ,&dipolar cycloaddition reactions of the tetracyclic species 5a with 2,3-dimethylbutadiene or mesitylnitrile oxide give rise to polycyclic products with differing skeletons (11 or 13 and 15, respectively). An X-ray crystal structure analysis of the cage compound 9a has been performed. Contribution to Organophosphorus Compounds. 101. For Part 100 see: Regitz, M.; Bergstrasser, U.; Hoffmann, A. Chem. Rev., in press.

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