Oxyphosphoranes, cyclic

These developments are derived from the early work of Ramirez and coworkers16 17, which was concerned with the formation of a type of cyclic oxyphosphorane that is formed by the addition of a trialkyl phosphite to either a diketone (Figure 5.8) or an a, 3-imsaturated carbonyl compound (Figure 5.9). Initially, developments from this effort... 

At this point it is profitable to consider the hydrolysis or alcoholyses of the cyclic oxyphosphoranes themselves. The trimethoxyphospholene (37) undergoes a nearly instantaneous reaction with one molar equivalent of water in benzene solution at 0°C101. The products of this reaction are mainly dimethyl phosphoracetoin and the cyclic methyl phosphate of acetoinenediol, viz-... 

A second type of five-membered cyclic oxyphosphorane is represented by derivatives of the 1,4,2-dioxaphospholane ring.111 These are made from the reaction of trivalent phosphorus compounds with certain aldehydes, for example 111... 

The scope of the transphosphoranylation reaction is enlarged by the availability of cyclic oxyphosphoranes (99) from the reaction of phosphites with certain dialkyl peroxides.14 Several cyclic and acyclic... 

The great flexibility of the trigonal bipyramidal skeleton displayed in the structures of many cyclic oxyphosphoranes suggests that the Berry pseudorotation mechanism may be an oversimplified representation for the permutational isomerisation of such species. Theoretical calculations and statistical considerations combined with these studies lead to the conclusion that this isomerisation may take place by a continuum of different routes (including turnstile rotation pathways) over a broad relatively flat potential surface, which have similar energy barriers. The Berry pseudorotation will, however, represent the energetically most favourable pathway for acyclic derivatives. 

Since then we have carried out X-ray and NMR studies (8-13) of a variety of cyclic oxyphosphoranes containing ring sizes from five- to eightmembered in an attempt to learn structural and conformational preferences as ring size varies and to understand what the important factors are that may induce structural and conformational changes. The results should prove useful in modeling proposed intermediates and activated states in a host of reactions that have been studied and for ones that may be developed in future work. 

An additional property of cyclic oxyphosphoranes of interest for mechanistic considerations is that they belong to a class of nonrigid molecules and undergo fast intramolecular ligand permutation as shown by our VT and NMR studies (8-12). Two processes are encountered, a so-called low temperature and high temperature process, illustrated here with five-membered ring containing phosphoranes. 

The above discussion emphasized phosphorinane ring orientation in isolated and structurally characterized cyclic oxyphosphoranes and their relation to proposed P activated states in enzyme reactions of cAMP. Here, we concentrate on ring conformation and its projected role in cAMP interactions based largely on our recent structural work and preliminary investigations of new systems. 

Recently, we synthesized the related phosphorane W and showed the formation of the (e-e) ring orientation by X-ray analysis (Prakasha, T. K. Day, R. O. Holmes, R. R., unpublished work). This represents the first solid state structural evidence of a diequatorial ring orientation in any cyclic oxyphosphorane system. However, when the phenyl ring substituents are replaced by protons. X-ray analysis of X (Prakasha, T. K. ... 

In conclusion, we may expect further advances in understanding factors controlling structural and conformational preferences of cyclic oxyphosphoranes, both from an experimental as well as a theoretical point of view. As the area continues to develop, the use of oxyphosphoranes as models in mechanistic interpretation should enhance our understanding of pathways followed in nucleophilic displacement reactions of tetracoordinated phosphorus compounds. Acknowledgment... 

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