Cyclic phosphinates, hydrolysis

Ring enlargement via hydrolysis of cyclic phosphonium salts obtained by alkylation (acylation) of cyclic phosphines. 

The cyclic thiophosphine products are very sensitive to hydrolysis by moisture giving the cyclic phosphine oxide in a 45% yield. 

Investigations by Cowley and coworkers and by Soottoo and Baxter have revealed that the reactions between 1,3-dienes and the phosphenium salts 123 (X = NPr 2 or Cl) proceed easily in dichloromethane at 0 °C, to give intermediate cyclic chlorophos-phonium salts (124) (compare structures 97, 119, 120 and 122), several of which were characterized spectroscopically and crystallographically. The highest yields of 124 (X = NPr 2) were achieved when R = R = Me and R = R" = H, and the lowest with the reverse pattern of substitution. The hydrolysis of the salts 124 (X = NR2), using NaOH in aqueous dioxane, yields the cyclic phosphinic amides 125 (X = NR2). 

Compound 290 was reacted with dichloro(phenyl)phosphine in the presence of Et3N this led to a ring-opening reaction with the breakage of the 0-CH2 bond, insertion of the phosphorus atom, and formation of the intermediate 291, which gave upon hydrolysis the cyclic phosphoryl-containing product 292 <1998IC4945>. 

The disecondary phosphines (41) and (42) (Scheme 3) are readily prepared by double P—Ph bond cleavage of dppe or dppp (for (41)) with lithium under ultrasonic irradiation, followed by aqueous hydrolysis.53,54 Disecondary phosphines PhPH(CH2)raPHPh (n = 2,3) have attracted recent interest for their use as starting materials for the preparation of multidentate and macro-cyclic ligands. Thus it has been shown that alkylation of the metal phosphide intermediate affords ditertiary or, in the case of (42), optically active tetra(tertiary)phosphines (see Section 1.12.2.12.1).55,56... 

The energies for structures along the reaction coordinate for hydrolysis of the bicyclic phosphinate [54] are detailed in Scheme 15. Analysis of the TBP intermediates and SP transition states for exocyclic cleavage in the base-catalysed hydrolysis of the cyclic urea phosphonate [24a] takes account of the increased effective electronegativity of the methylene ligand in this system (Scheme 16). The calculations for [24] vividly illustrate that what is perceived as a disallowed pseudorotation is shown to be energetically favourable by careful analysis and application of relative apicophilicities. 

Cyclic Phosphoranes - The reaction of dioxetanes (28a-c) with ylides (29a-d) gave phosphonium alkoxides (30a-f) in equilibrium with the pentacoordinate dioxa-2,5-phosphorinanes (31a-f).16 Hydrolysis via the hydroxyphosphoranes (32a-f) gave the phosphine oxides (33a-f). 

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