Ring Containing Phosphoranes

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. 

Rings containing Nitrogen. - The reactions of aziridines with alkylidene-phosphoranes and with phosphorus(III) nucleophiles and the reactions of... 

In contrast, the geometry of the dioxadithiaspirophosphorane (8) is essentially rp (93% distorted from tbp) with the chalcogen atoms occupying the basal positions, a structure which represents the least distorted rp phosphorane on record. The paper re-emphasizes that no example of a rp structure for five-membered cyclic phosphoranes exists unless two rings are present, the rings contain unsaturation, and like atoms are present in any one ring bound to... 

The pentacoordinate intermediate is the analog of the tetrahedral intermediate, and stable phosphoranes are the analogs of ortho esters and related species in carbon chemistry. Ph3P(OPh)2 and P(OPh)5 were reported in 1959, and in 1958 a general synthesis of pentaalkoxy phosphoranes containing an unsaturated five-membered ring was reported. In 1964 a synthesis of pentaethoxyphosphorane was devised which led to the preparation of a number of saturated and unsaturated pentaalkoxy... 

Two series of phosphoranes (86 or 87) containing a dioxaphos-pholene ring and a 2-phospholene or 3-phospholene ring have been synthesised from trico-ordinate phospholenes (83) or (84) and 1,2-dicarbonyl compounds (85)1 7. The compounds were characterised by analysis, XH and J1P n.m.r. and, in contrast to earlier work,1 8 were found to be stable towards the retrodiene fragmentation. 

Treatment of a seleno-subsitituted phosphorane 219 containing a diazaphosphetidinone ring with bis(2-chloro-ethyl)amine hydrochloride and triethylamine gave the spirophosphorane 220 in 21% yield (Equation 43) C1995ZFA2001, 1997ZFA1325>. 

Details77 have appeared of the synthesis of fiuorophosphoranes containing four-membered rings,78 and extensive variable-temperature n.m.r. studies have been described. Thus, for the phosphorane (82), the most stable conformations are (83) and (84), which inconvert to a minor conformer (85), via the intermediate (86).77... 

Methods for preparation of phosphoranes and spirophosphoranes containing a l,3,2A5-oxazaphosphetidine ring from trifluoroacethylphosphoramidites have been developed <1995RJC198, 1997RJC151>. 

Experiments with aspartic acid have shown that only a-aspartic acid dipeptides are formed [123], which is consistent with the transformation of the substrate into a pentacoordinated phosphorane mixed anhydride 17 [24] containing a five-membered ring through a self-activation process. 

Scheme 3 contains several of the fundamental structures with penta-valent phosphorus, among them phosphorane itself, PH6 (21), and pentahydroxyphosphorane, P(OH)6 (26). The latter is the hydrate of phosphoric acid H3P04+H20 - P(OH)5. A hydrate of methylphos-phonic acid (CH3)(HO)4P (29), is also included as a model for its esters. Mono- and di-ionized forms, (27), (28), (30), are also given, since their stabilities in various isomeric forms provide important data concerning the role of intermediate oxyphosphoranes in the chemistry of phosphoric acid and its derivatives. A model compound of the 1,2-oxaphospholene ring (31), is provided, since this system, in the form of several derivatives, will be discussed extensively in Section VIII. 

A possible explanation of these differences is that the reactions of the trivalent phosphorus compounds with carbonyl compounds may contain reversible and irreversible steps. The condensation of one mole of biacetyl with one of the phosphite probably contains several reversible steps leading eventually to the 1 1 oxyphosphorane. If this 1 1 adduct is of high energy as a result of ring strain and/or intramolecular crowding in the TBP, it might not be observable. The carbon-carbon condensation step in the formation of the 2 1 adducts is probably essentially irreversible under most conditions hence, once that step is achieved, there is an opportunity for isolation of the 2 1 phosphoranes. 

Bicvclic and Tricyclic Phosphoranes The first synthesis of a series of pentaco-ordinated structures (82a-d) containing a three-membered (phosphirene) ring has been achieved by the oxidative addition of tetrachloro-o-benzoquinone... 

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