Heterocyclic compounds Cyclic organic five-membered

The central Co,=Cp double bond of an allenylidene backbone can also react with a variety of dipolar organic substrates to yield cyclic adducts. Most of the cychza-tion processes reported occur in a stepwise manner via an initial nucleophilic attack at the Coi atom and further rearrangement of the molecule involving a coupling with the Cp carbon. Representative examples are the reactions of the electron-poor ruthenium-allenylidene complex 46 with ethyl diazoacetate and 1,1-diethylpropar-gylamine to yield the five- and six-membered heterocyclic compounds 82 and 83, respectively (Scheme 29) [260, 284]. 

Unlike epoxides, these five-membered heterocyclics have received scant attention from organic chemists. But the recent catalytic asymmetric dihydroxylation of alkenes (14, 237-239), which is now widely applicable (this volume), and the ready access to optically active natural 1,2-diols has led to study of these compounds, including a convenient method for synthesis. They are now generally available by reaction of a 1,2-diol with thionyl chloride to form a cyclic sulfite of a 1,2-diol, which is then oxidized in the same flask by the Sharpless catalytic Ru04 system, as shown in equation I.1... 

Organoiodine(V) compounds are represented by several common classes shown in Figure 1.3 all these compounds have found application as efficient oxidizing reagents. Particularly important in organic synthesis are noncyclic iodylarenes 18, numerous five-membered heterocyclic benziodoxole derivatives 19 and 20, including IBX and DMP (Table 1.1), pseudocyclic iodylarenes 21-23 and cyclic or pseudocyclic derivatives of 2-iodylbenzenesulfonic acid, 24-26. 

The unique combination of double bonds in the molecules of those compounds, each with different reactivity along with the easy preparation, makes phosphorylated allenes useful substrates for the synthesis of different cyclic and noncyclic organophosphorus compounds. Recent investigations increase the scope of application of phosphorylated allenes as precursors in organic syntheses. Most of them are accompanied by the formation of five- or six-membered phosphorus heterocycles, which in many cases demonstrate certain biological activity. 

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