Phosphonium amalgam

An Quecksilber konnen sich in aprotischen Losungsmitteln analog den Ammonium-Verbindungen auch mit Phosphonium-Salzen Phosphonium-amalgame bilden (vorwie-gend bei der Reduktion entsprechender Jodide)5. 

Sodium-naphthalene reduction of organotrineopentoxyphosphonium salts led to the instantaneous loss of phosphonium ion phosphonates and phosphites were obtained748 (reaction 224). Alkali metal amalgams are efficient reagents for the reductive cleavage of both achiral and optically active phosphonium salts configuration is retained750 (Table 23). 

When the reactions of pyrroles and indoles with aldehydes are catalyzed by hydriodic acid, the initially formed carbinols or azafulvenes are reduced to yield the corresponding alkylpyrroles and alkylindoles (68CJC3291,70CJC139). The reductive alkylation of the pyrrole ring, using a range of aliphatic and aromatic aldehydes and ketones, may also be accomplished with phosphonium iodide, with hydrochloric acid and zinc amalgam, or with tin(II) bromide in hydrobromic acid. 

Metals such as Na or alkali metal amalgams can also be used in the cleavage of the C—P" bond. In the latter case, reductive cleavage of achiral and optically active quaternary phosphonium salts succeeds in high yields with retention of configuration. ... 

The reductive cleavage of achiral and optically active quaternary phosphonium and arsonium salts with alkali metal amalgams to form tertiary phosphines and arsines succeeds in high yield with retention of configuration [124]. The reduction with the amalgams was found to give better yields than the conventional cathodic cleavage. 

Dimsylsodium (24) functions as a highly basic sulfur ylide. It can be used to convert phosphonium salts to phosphorus ylides for use in the Wittig reaction. Dimsylsodium also reacts with aldehydes and ketones by nucleophilic addition to form epoxides and with esters by nucleophilic substitution to yield p-ketosulfoxides (25) (Scheme 11). The p-ketosulfoxides (25) contain acidic a-hydrogens which can be readily removed to allow alkylation, and the products (26) suffer reductive desulfuration on treatment with aluminium amalgam to yield ketones (27) (Scheme 11) This procedure can, for instance, be applied to the conversion of ethyl benzoate to propiophenone (28) (Scheme 12). 

Sodium amalgam-reduction of the salt (69) (obtained from the reaction of acyl-stabilized ylides with trifluoromethane sulphonic anhydride) provides a new synthesis of acetylenes (Scheme 11). A new synthesis of ethynyltriphenyl-phosphonium salts (70) is provided by the reaction of acylmethylenetriphenyl-phosphoranes with dibromotriphenylphosphorane and base. ... 

ALKENES Calcium amalgam. N,N-Dimethylformamide dimethyl acetal. N,N-Methylphenylaminotriphenyl-phosphonium iodide. N,N,N, NrTetra-methyldiamidophosphorochloridate. Titanium(O). p-Toluenesulfonylhydra-zine. Tii-n-butyltin hydride. Triphenyl-phosphine-Diethyl azodicaiboxylatc. Trityl tetrafluoroborate. 

Unlike the corresponding phosphonium salts, addition of sulfonium salts to aldehydes results, not in the alkene products, but in the formation of epoxides (see Section 1.1.5.2). However, sulfones can be used to prepare alkenes, by way of the a-metallo derivatives, in what is termed the Julia olefination (alkenylation). Addition of the organometallic species to an aldehyde or ketone gives a p-hydroxy sulfone which, in the form of its 0-acyl or 0-sulfonyl derivative, undergoes reductive cleavage with, for example, sodium amalgam in methanol to form the alkene. The reaction is regioselective and can be used to prepare mono-, di- and trisubstituted alkenes (2.91). 

Baeyer had previously introduced the important method of reduction by heating with zinc dust. He used phosphonium iodide (a good method of preparation of which he described) instead of hydriodic acid and red phosphorus (Berthelot s method) in reductions. He carried out a long research on the reduction of phthalic, isophthalic, and terephthalic acids with sodium amalgam, the results being used in elucidating the structure of benzene (see p. 804). Isophthalic acid derivatives were synthesised by O. Doebner. ... 

Cottrell, W.R.T., Morris, R. A. N. Quaternary phosphonium and tertiary sulphonium amalgams. Chem. Commun. 1968,409. 

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