Phosphonium salts unsaturated

The present preparation illustrates a general and convenient method for the fnms-iodopropenylation of an alkyl halide.4 The iodopropenyl-ated material is not usually stable but is a useful synthetic intermediate. For example, it forms a stable crystalline triphenylphosphonium salt for use in the Wittig reaction, and under Kornblum reaction conditions (DMS0-NaHC03, 130°, 3 minutes) it gives an (E)-a,/9-unsaturated aldehyde.4 In addition to the phosphonium salt described in Note 15, the following have been prepared (4-p-methoxyphenyl-2-butenyl)-triphenylphosphonium iodide [Phosphonium, [4-(4-methoxyphenyl)-2-butenyl]triphenyl-, iodide], m.p. 123-127° (2-octenyl)triphenyl-phosphonium iodide [Phosphonium, 2-octenyltriphenyl-, iodide], m.p. 98° and (2-octadecenyl)triphenylphosphonium iodide [Phosphonium, 2-octadecenyltriphenyl-, iodide], m.p. 50°. 

The bis-phosphonium salt (156) has been condensed with various dialdehydes to give potentially aromatic and anti-aromatic systems, while fully unsaturated 11- (158), 12- (159), and 13-membered (160) sulphur heterocycles have been prepared as shown. These showed no appreciable ring current and are presumably non-planar. 

Phosphonium salts can be synthesized by the transition-metal-catalyzed addition reaction of triaryphosphines and acids to unsaturated compounds. The reaction of PPh3, CH3SO3H, and alkynes in the presence of a palladium or rhodium catalyst gave alkenylphosphonium salts. Although Pd(PPh3)4 directed the C-P bond formation at the internal carbon atom of aliphatic 1-alkynes (Markovnikov mode), [RhCl(cod)]2... 

It is interesting that the reaction of triphenylphosphine with a 1,2-allenyl ketone leads to the formation of a vinyl phosphonium salt 449, which upon protection of the carbonyl group would accept nucleophilic attack followed by elimination in the presence of Et3N to afford y-nudeophile substituted- ,/j-unsaturated enones 451 [197]. 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

Preparation, properties and reactions of phosphonium salts TABLE 3. 31P chemical shifts (ppm) of unsaturated phosphonium salts... 

FIGURE 2. Resonance structures in a,/l- and / ,y unsaturated phosphonium salts... 

R3PCH=CHCH=CH2 Clin the same way, in the case of the propargylphosphonium salt, two successive isomerizations of the unsaturation from the / ,y to the opposition, combined with a Michael-type addition of nucleophiles on the intermediate allenyl phosphonium, afford various /Mieterosubstituted oc,/ -unsaturated phosphonium salts, which have found interesting applications in organic synthesis (reaction 44). 

Dehydrobromation of halogenated phosphonium salts is currently used in the synthesis of unsaturated compounds, (cf. Section II.C) provided that a labile carbanion is created in a suitable position relative to the halogen atom (reaction 261). Such bases as Et3N (for / - or (5-halogenated phosphonium salts)288 or bromide anion357 may induce this elimination. Fluorine atoms of the cationic part of 3-methyl-1,1-difluorocyclopent-2-ene-1-phosphonium hexafluorophosphate were substituted when the compound was treated with absolute methanol under mild conditions412. 

When unsaturated ketones are used as reactants, the C=C bond is preferentially reduced. Most of the complexes are transformed and thus deactivated after their first catalytic run. The phosphane (tppts) of the complexes underwent reactions with the organic products, giving phosphonium salts, which are responsible for the deactivation. The analysis of the aqueous phases shows that the recycling would be difficult in many cases. 

Other oxazine-based reagents, such as the phosphonium salt (741) prepared from 2-chloromethyl-4,4,6-trimethyldihydro-l,3-oxazine (740), have been used in Wittig reactions to synthesize a,/3-unsaturated aldehydes or acids (Scheme 170) (74JOC623). 

This type of disconnection is mainly used for the preparation of dipeptides of type Xaai >[ , CH=CH]Gly. It allows control of the stereochemistry of the Xaa residue by starting from chiral a-amino aldehydes. For the construction of the /ram -p,y-unsaturated carboxylic acid moiety, the use of the triphenylphosphonium salt 31 (Scheme 9) derived from 3-chloro-propanoic acid was not suitable.14 Instead, the trimethylsilylprop-2-ynyl phosphonium salt 33 serves as a three-carbon unit, which can be converted into the P,y-unsaturated acid by hydroboration and oxidation. The required Boc-protected a-amino aldehyde 32 can be prepared using virtually racemization-free procedures. 37 However, at the end of the reaction sequence, racemization has been detected, especially for Boc-Phet )[ , CH=CH]Gly-OH, but not for the Ala and Pro analogues. 63 A mixture of E- and Z-enynes 34 and 35 is formed (8 2 to 9 1), which can be separated by column chromatography. 4,48 50 53 64 65 ... 

In contrast to a,(3-unsaturated phosphonium salts, ot,(3-unsaturated phosphonates (161)1331 alkylate ali-cyclic ketone enolates efficiently, while the homologous diethyl butadiene phosphonate (162)133bintramolecular cyclization. Heathcock reports that... 

The preparation of the y-thioacetalated phosphonium salts 2 takes place in a one-pot reaction by addition of triphenylphosphi-ne hydrobromide on the a,P-unsaturated carbonyl compound and subsequent thioacetalation (28, 29) ... 

The phosphonium salts (58) were versatile reagents for the synthesis of 1,2,3-thiadiazoles (59) with unsaturated side chains. Ring closure of triphenylphosphonium chlorides (57) by the Hurd and Mori method gave these salts (58). Subsequent Wittig reactions did not occur stereoselectively. [95ZN(B)1121]... 

The reaction of the phosphonium salts 28, generated from the -halogencarboxylic esters 26, with sodium ethoxide in DMF or sodium hydride in DMSO yields the phosphoranes 29 which, on treatment with aldehydes 30, are converted into (Z)-alkenoic esters 31 49,51 53). To synthesize As-unsaturated acids and higher homologous acids of type 31 (m 11) Bergelson et al. 49,54) olefinated ethyl co-formyl-alkanoates 34, obtained from co-iodoalkanoic esters 32, with alkylidenephosphoranes 35 to the ethyl esters 31 (Scheme 7). 

Similar reactions lead to dehydroflexixanthin 566 272) and p,(3-carotene-2,2 -diol 567 273). Polyenes like 570 used in the combat against tumor, can be obtained from the phosphonium salt 568 and the formylpolyene ester 569 274). Applying the Wittig reaction, also branched unsaturated cross-conjugated carotenals 571 275) and the polyene derivative 572 276> can be prepared (Scheme 96). 

Reaction of the ylide, generated from the phosphonium salt 578 (from the alcohol 577 and phosphine hydrobromide 504), with the polyene aldehyde 542 gives aleuria-xanthin acetate 579218). The methyl ester of the naturally occurring bixin 586 is formed by a combination of some carbonyl olefinations 279). The acetoxyaldehyde 580 is olefinated with methoxycarbonylmethylene-triphenylphosphorane 67 to the ( )-unsaturated ester 581. The latter is converted into the phosphonium salt 582 upon treatment with triphenylphosphine hydrobromide 504. The corresponding ylide of 582 is reacted with the dialdehyde 539 to the polyene aldehyde ester 583. The latter is reduced and converted into phosphonium salt 584. The corresponding ylide is now reacted in a third carbonyl olefination with 585 to give the methyl ester 586 279> (Scheme 98). 

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