Phosphorinanes conformation

Phosphorinane, 4-t-butyl-1 -phenyl-synthesis, 1, 500 Phosphorinane, I-chloro-synthesis, 1, 500 Phosphorinane, 1-hydrocarbyl-I-sulfide synthesis, 1, 500 Phosphorinane, 1-phenyl-synthesis, 1, 499 Phosphorinanes, 1, 497-506 bicyclic bridged derivatives synthesis, 1, 501 conformation, 1, 503-504 NMR, 1, 497 oxidation, 1, 498 reactions, 1, 497 structure, 1, 497, 503-504 sulfuration, 1, 499 synthesis, 1, 499... 

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... 

The geminal coupling of some azo1ooxaphospho1enes is reported to correlate with A.. 9 1 Vicinal couplings have been used in the conformational analysis of a variety of compounds such as dioxaphosphorinanes,92 phosphorinanes (in combination uith CNDO/2 calculations),93 and bromophosphorinanes (in combination uith dipole moment measurements).99 The various couplings for 1,1-viny1idene-diphosphonic acid and its salts have also been measured.95... 

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... 

Unlike 1,3,5-dioxaphosphorinanes the relative population of the con-former with the axial phenyl group at phosphorus decreases in 1,3,5-diazaphosphorinanes both for P(III) and for P(IV) compounds. Conformational analysis of 5-phenyl-1,3,5-diazaphosphorinanes and their oxides, sulfides, and selenides showed that the conformational equilibrium shifted toward the conformer with the axial phenyl group on changing from P(III) to P(1V) derivatives. The same conclusion made for 5-phenyl-l, 3,5-dioxaphosphorinanes, but it is contrary to that made for 1-phenyl-phosphorinane-4-ones and their derivatives (83MI1). 

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). 

In other substituted phosphorinanes the HNMR spectra are too complicated for a clear-cut conformational (and configurational) analysis. Even in 1-methylphosphorinane the H atoms of the 1-Me group appear as two multiplets due to coupling with the (a) and (e) H atoms of C-2 and C-6. However, the (a,a), (a,e) and (e,e)4/H-h coupling constants are too similar to allow conformational analysis by H NMR. We shall see later that 13C NMR is an excellent method for solving these problems. 

The diagnostic coupling constant /P c for conformational analysis of phosphorinanes (P-CN = 3) is lost with phosphorinanes where P-CN = 4. Shifts and /P c values of two non-rigid and two cis-trans rigid phosphorinane 1-oxides and 1-sulfides should be studied for comparison (Tables 2 and 3). The large differences between the two classes are then evident. 

A detailed ab initio and modified neglect of diatomic overlap (MNDO) study of structural parameters and pyramidal phosphorus atom inversion and also enthalpy differences between the participants in the conformational equilibrium (axial and equatorial) of 1-R-phosphorinanes (R = H, CH3, C2H5) has been investigated and is in good agreement with the observed NMR and X-ray values <1999IJB660>. 

Investigation of the conformational equilibrium of 1-methyl-phosphorinane (4) by low temperature and P-nmr shows a temperature dependence, favouring the equatorial methyl conformer at low temperature and the axial methyl one at room temperature (S.I. Featherman and L.D. Quin, J. Amer. chem. Soc., 1973, 95, 1699). 

C-nmr spectral data have been used to show that 1-methyl-and 1-phenyl-phosphorinane and their 4-ones, related 1-oxides and 1-sulphides and 1,1-dimethylphosphorinanium salts, possess similar chair conformations to those of the analogous S, O, and N six-membered heterocycles (J.A. Hirsch and K. Banasiak,... 

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. 

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. 

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