Bicyclic and Tricyclic Phosphoranes

The section begins with reports of two mechanistic studies relevant first to phosphate ester hydrolysis and secondly to an olefin-forming reaction akin to the Homer-Wadsworth-Emmons reaction but involving a spirooxyphosphoranyl 

The second mechanistic paper involved the reactivity of carbanions a to pentaco-ordinated phosphorus in spirooxyphosphoranes. In particular, the reaction of 39 with benzaldehyde at — 78 °C was studied in detail. The products were 40 and a mixture of E and Z alkenes (41 a,b). The preliminary mechanistic results suggested that the E,Z selectivity was determined by a combination of kinetic and thermodynamic control. 

Reaction of the nitrile-imine 42 with the phosphonite 43 gave the bicyclic phosphorane 46 via intermediates 44 and 45. The structure of 46 was confirmed by elemental analysis, IR, H/ P nmr and finally X-ray crystallography which revealed that the bicyclic structure was almost planar.  

Reaction of the benzoxazaphospholine 47 with the hydroxymethyl bicyclic phosphite 48 gave the polycyclic compound 51 by dimerisation of the intermediate 50. A similar reaction of 47 with pentamethylene diol (52) gave an unsymmetrical spirophosphorane (54) with a P-C bond via 53.  

In a continuation of earlier studies, Malenko et al. have shown that bromina-tion of tris(N-trifluoroacetylamide)-phosphine (55) gives a mixture of bicyclic 

Reaction of PCI5 with u-aminophenol (47) under controlled temperature conditions gave the spirophosphorane (48) but at higher temperatures a bisphosphorane (49) was isolated and characterised by X-ray crystallography.  

Multinuclear ( H, C, P and N) NMR studies have been reported for three hydrophosphoranes, (50a-c), derived from o-aminophenols. Selective hetero-nuclear H [ N] double resonance experiments and 2-D N/ H HETCOR experiments enabled the determination of the signs of various coupling 

Molecular modelling of 40 complexes derived from ten bicyclic phosphoranes (51-60), and the alkali cations, Li , Na and has been carried out using the Insight II V97 programme based on the ESFF force field/ Calculations were 

Reaction of (R)-2-aminobutan-l-ol (61) with P(NEt2)3 gave a mixture of the diastereomeric phosphoranes (62ab) in a ratio of 3 7 (a b). Multinuclear ( C, N) NMR, IR and mass spectrometry studies were reported and X-ray crystallographic analysis of (62b) revealed a slightly distorted tbp with apical oxygen and equatorial nitrogen atoms.  

The reaction of the P-H bond of spirophosphoranes (68) and (69) with long chain imines, (70a-h), occurs instantaneously at room temperature and leads to the formation of a-aminoalkyl spirophosphoranes (72a-h) and (73e), with a high degree of diastereoselectivity in most cases. With R = Ph the observed diastereoselectivity was between 80 and 90% as determined by and P NMR but dropped to 65% for R = Me in (72g). The authors proposed a 

In a continuation of their momentous work on the structure of hypervalent molecules, Holmes et al have reported the synthesis and structure (by X-ray crystallography) of a unique geometry in a pentacoordinate tetraoxyphosphorane 

The C-spiroxyphosphorane (42) is selectively deprotonated by LiHMDS at — 78°C to the lithiated a-anion (43) which on reaction with methyl iodide gives 

An extensive report by Segall at the Jerusalem conference showed that bis-(o-carboxyaryl)methylphosphine oxides (48) and bis-(o-amidoaryl)methylphosphine oxides (49) cyclodehydrate in acidic media to give tbp spirodioxaphosphoranes 

Intramolecular cyslisation of the phosphine oxide (64) with the Mitsunobu reagent gave the l,2,X -azaphosphetidine (65) which was characterised by 

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Pentacoordinated and Hexacoordinated Compounds 4 Bicyclic and Tricyclic Phosphoranes... 

Novel bicyclic (92) and tricyclic (93ab) hydrophosphoranes have been synthesized and shown to form complexes with PdCl2(COD), PdCl2(RCN)2, and Pd(allyl)Cl2 containing an open form of the phosphoranes. The Pd-catalyzed alkylation of 1,3-diphenylallyl acetate (94) with dimethyl malonate gave (95) in up to 74% ee using complexes of (92) or (93ab). " ... 

Bicyclic phosphoranes (87a-d) prepared by the reaction of (85a-d) with (86) were isolated and then characterised by m.s., elemental analysis, i.r. and multinuclear n.m.r. spectroscopy no pseudorotation was observed at ambient temperature. In a related study, tricyclic phosphoranes (89a-d) were obtained from the reaction of (88a-d) with (86). An analogous reaction between (90a-i) and (86) furnished another series of tricyclic phosphoranes (91a-i). The single crystal X-ray structure of (91a) revealed a tbp configuration about phosphorus with a 26% distortion along the Berry coordinate using P-01 as the pivot. 

At present, cyclic phosphoranes have been classified into four main families (Figure 4) monocyclic, bicyclic (spiro and fused), tricyclic and tetracyclic. 

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