Phosphorinane ring conformation

By way of molecular orbital calculations, we have examined various phosphorinane ring conformations in both (a-e) and (e-e) orientations in a TBP geometry and have obtained final geometries and energies for saturated five- and six-membered rings in the oxyphosphorane molecules 1 - o. 

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. 

The l-phenyl-4-phosphorinan ring (3) has a chair conformation with the phenyl group axial. This conformation is retained when the oxygen atom is replaced by two methyl groups. " Bond lengths are angles are normal. 

The n.m.r. spectra of a series of simple derivatives of 2-oxo-l,3,2-dioxa-phosphorinan have been reported, analysed, and discussed in terms of ring conformations. This paper draws attention to a type of deceptively simple ABX spectrum found in this type of compound. 

N.m.r. spectroscopy has played an important part in determining the stereochemistry of the 1,3-dioxaphosphorinanes (52). The presence of the saturated six-membered ring means that there are usually conformational effects to be unravelled before configurational assignments can be made. The chair conformation is generally dominant. Phosphorus substituents which exhibit shielding effects show that in many P " phosphorinanes this substituent occupies an axial position and Sis( has been used to establish the equatorial conformation of a t-butyl substituent at C(5). Even in P" derivatives the isomer possessing the bulkiest P-substituent in an axial... 

Two heterocyclic systems have been investigated - the 1,3,2-dioxaphosphepene (45) and its oxide,13 1,3,2-dioxa-phosphorinanes and their oxides, sulphides and selenides (46).136,137 Three ring vibrations were involved in the conformational study of the amides (46, Y = NR2).137... 

Phosphorinanes (1), R being H, alkyl, aryl, halogen, OR, NR2 and others, are known. Like open chained P compounds of CN = 3, most of these compounds are air sensitive and non-crystalline. The six-membered ring is nearly always in a chair conformation. Both structures (la) and (lb) are possible, R being axial (a) or equatorial (e). 

Chair-shaped six-membered rings, fixed in one conformation, occur in numerous crystalline phosphorus compounds, for example, black phosphorus (Chapter 4.1), trimetaphosphate and cyclo-hypophosphate salts (Chapter 5.3), hexameric phenylphosphine and various phosphorinane derivatives (Chapter 6.20). 

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