Diphosphonium salts

A number of NH phosphinous amides have been P-alkylated by previous conversion to their corresponding anions [59,74]. A particular case of double alkylation takes place with the anion derived from the AT-phosphino phosphinous amide NH(PPh2)2 yielding the diphosphonium salt 17 [102] (Scheme 17). When neutral, its methylation is reported to give the P-H phosphazene-phos-phonium salt 18 [103]. 

Stimulated by the biosynthetic pathways, biomimetic heterocyclization methods have also been developed with high efficiency. For example, using an oxo-bridged diphosphonium salt prepared in situ from PhsPO and Tf20, a variety of hetero-... 

Similarly to the synthesis of 304-308, bicyclic diphosphine 317 with two bridgehead phosphorus atoms was synthesized from tricyclic diphosphonium salt 313 by the reduction with KBH4 <2000AGE2879>. 

Mukaiyama, T, Suda, S, Diphosphonium salts as effective reagents for stereoselective synthesis of 1, 2-cA-ribofuranosides, Chem. Lett., 1143-1146, 1990. 

The rates of acid-catalysed cyclization of certain alkynylphosphines to the cyclic diphosphonium salts (141) have been studied, and a mechanism has been proposed... 

The dinuclear dicationic complex 7 with the di-ylide [(Ph3PCH)2CO] as a bridging ligand between two silver atoms has been obtained from a transylidation reaction between the diphosphonium salt [(Ph3PCH2)2C0]C104 and the bis(yhde) complex [Ag (Ph3P)CHC(0)CH3 2]ClC>4 described above (equation 7)19. 

Macrolides and Related Compounds. - Complex phosphonates continue to be used in the construction of carbon skeletons and in cyclisation reactions, as exemplified by the synthesis of didesepoxyrhizoxin, the biogenetic precursor of the antitumour agent rhizoxin, via intramolecular olefination of (225). (+)-Trienomycins A and F, members of a family of ansamycin antibiotics, have been synthesised using a double Wittig reaction of the diphosphonium salt (226) as a key step. The reaction produces a mixture of isomers including 21% of the required (all- ) product. 

Organophosphonium salts are a general class of compounds which are difficult to analyse via conventional EI-MS Thus several reports have appeared in the literature which describe the use of alternative ionization methods to analyse this important class of compounds " Early studies, which centered around the use of field desorption (FD), demonstrated that the intact phosphonium ion is often the most abundant ion. A comparison was made between the use of FD and FAB as ionization methods for the analysis of the diphosphonium salt FD produces high abundances of the intact phosphonium ions [M - Br ] and [M - 2Br ], whereas these ions are only minor peaks in the FAB mass spectrum using glycerol as the matrix. Instead, the fragment ion 35 is the base peak in the FAB spectrum. 

The reaction of Tf20 with PhsPO in CH2CI2 at 0°C affords triphenylphosphine ditriflate, which can be used as an oxygen activator, and then to a diphosphonium salt (eq 35). ... 

Polymers with triazole groups act to enhance the electroluminescent efficiency when used in two layer devices with PPV as a hole-transporting emitter. PPV-hased copolymers bearing an electron-withdrawing triazole unit in the main chain can be synthesized by the Wittig reaction between triazole diphosphonium salt and the corresponding dialdehyde monomers, respectively. ... 

Since deprotonation of the C o-diphosphonium salt tends to eliminate PPhs instead of forming the diphosphorane, this Wittig reaction with the C 15-aldehyde must be carried out at low temperatures. In contrast, the first approach, using a Ci5-phosphonium salt and the Cio-dialdehyde, gives higher and more reproducible yields even at ambient temperature. 

The acetylenic diol 1 has been used for the preparation of the phosphonium salts 9 (route 7 —and 10 (route 7 7772 70) which have been applied to the synthesis of p,p-carotene (3) [6]. The phosphonium salts 9 and 70 also proved their utility in the syntheses of 7,8-didehydroastaxanthin (402) and 7,8,7 ,8 -tetradehydroastaxanthin (400) [7] and of optically active carotenoids with 3,5,6-trihydroxy-5,6-dihydro-p-end groups [8]. Despite these interesting examples it is noteworthy that, in general, the diphosphonates are much better reagents for double olefination than the corresponding diphosphonium salts [9]. 

Recently, 118 was applied to the synthesis of (9Z,9 Z)-lycopene [(9Z,9 Z)-31] [42]. The (2Z)-ester 118 was transformed into (2Z)-4,5-didehydrofarnesal (119) by reduction of 118 with DIBAH and oxidation of the intermediate allylic alcohol with Mn02. An inverse Wittig condensation of 119 with the Cio-diphosphonium salt 10 gave an isomeric mixture from which pure (9Z,9 Z)-lycopene [(9Z,9 Z)-31] was isolated after isomerization and crystallization from hexane (see Chapter 3 Part V). 

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