Triphenylphosphonium compound

Fig. 5-51. Separation of various n-alkyl triphenylphosphonium compounds. -Separator column Inertsil ODS II (5 pm) eluent 0.002 mol/L HQ / acetonitrile (72 28 v/v) flow rate 0.8 mL/min detection suppressed conductivity com-...

Bravo et al. studied the reaction of various ylides with monooximes of biacetyl and benzil. Dimethylsulfonium methylide and triphenylarsonium methylide gave 2-isoxazolin-5-ol and isoxazoles, with the former being the major product. Triphenylphosphonium methylide and dimethyloxosulfonium methylide gave open-chain products (Scheme 135) (70TL3223, 72G395). The cycloaddition of benzonitrile oxide to enolic compounds produced 5-ethers which could be cleaved or dehydrated (Scheme 136) (70CJC467, 72NKK1452). 

The discovery of junipal focused the attention of Sorensen, who had been investigating the occurrence of polyacetylenes in Com-positae, on the possibility that these acetylenes were accompanied by thiophenes. From Coreopsis grandiflora Hogg ex sweet, 2-phenyl 5-(1-propynyl) thiophene (240) was isolated and its structure confirmed by synthesis of the tetrahydro compound, 2-phenyl-5-n-propyl-thiophene. From the root of tansy, the cis and trans isomers of methyl 5-(l-propynyl)-2-thienylacrylate (241) have been isolated. The total synthesis of trans (241) was achieved by reacting junipal with methylcarbethoxy triphenylphosphonium bromide (Wittig reaction) Several monosubstituted thiophenes, (242), (243), and... 

There have been some reports of the use of N-sulfinyl compounds to transfer both a nitrogen and a sulfur atom. An example is the reaction of N-sulfinylcyclohexylamine (59 R = cyclohexyl) with diphenylcyclopropenone in the presence of nickel tetracarbonyl. An isothiazolinone S-oxide (62) was the product.80 Similarly, A-sulfinyl-/>-toluenesulfonamide (59 R = tosyl) and the Wittig reagent triphenylphosphonium phenylbenzoylmethylide give 1,2,3-thiadiazoline (63).8 ... 

The ylide obtained from (methyl)triphenylphosphonium bromide reacts with morpholine derivatives 597 to give phosphonium salts 598 which upon treatment with -butyllithium are converted to new ylides 599. In a reaction with aldehydes, ylides 599 form iV-(l,3-disubstituted allyl)-morpholines 602 (Scheme 94) <1996AQ138>. Another less common nucleophile that can be used for substitution of the benzotriazolyl moiety in Af-(a-aminoalkyl)benzotriazoles is an adduct of iV-benzylthiazolium salt to an aldehyde which reacts with compounds 597 to produce adducts 600. Under the reaction conditions, refluxing in acetonitrile, salts 600 decompose to liberate aminoketones 601 <1996H(42)273>. 

The attack of the nucleophile on the acceptor-substituted allene usually happens at the central sp-hybridized carbon atom. This holds true also if no nucleophilic addition but a nucleophilic substitution in terms of an SN2 reaction such as 181 — 182 occurs (Scheme 7.30) [245]. The addition of ethanol to the allene 183 is an exception [157]. In this case, the allene not only bears an acceptor but shows also the substructure of a vinyl ether. A change in the regioselectivity of the addition of nucleophilic compounds NuH to allenic esters can be effected by temporary introduction of a triphenylphosphonium group [246]. For instance, the ester 185 yields the phos-phonium salt 186, which may be converted further to the ether 187. Evidently, the triphenylphosphonium group induces an electrophilic character at the terminal carbon atom of 186 and this is used to produce 187, which is formally an abnormal product of the addition of methanol to the allene 185. This method of umpolung is also applicable to nucleophilic addition reactions to allenyl ketones in a modified procedure [246, 247]. 

Anomeric triphenylphosphonium salts have been used as well as phenylsul-fides,but in the latter case extra stabilization is necessary (see below). Anomeric nitrosugars, which have been extensively studied in C-glycosylation reactions by Vasella, will be covered in Sect. 2.2.1 and ester enolates derived from 3-deoxy-2-ketoulosonic acids (sialic acid and KDO derivatives), which bear a structural similarity to 2-deoxy pyranosides, will be covered in Sect. 4.4. Deprotonation of anomeric phenylsulfones has been discussed in Sect. 2.1.1 and additional transformations on closely related compounds are presented in Scheme 14 [20]. Alkylation of phenylsulfone 54 with epoxide 55 provides adduct 56 which eliminates benzenesulfinic acid at room temperature to give the C(l)-alkylated glycal 57 a similar elimination is also observed with adducts derived from... 

The other stereoselective synthesis/281 shown in Scheme 8, foresees conversion of Boc-L-Asp-OtBu 20 into the related (3-aldehyde 22 via the Weinreb amide 21 and its reduction with diisobutylaluminum hydride (DIBAL-H). Wittig condensation of 22 with the ylide derived from (3-carboxypropyl)triphenylphosphonium bromide using lithium hexamethyldisilaza-nide at —78 to 0°C, produces the unsaturated compound 23 which is catalytically hydrogenated to the protected L-a-aminosuberic acid derivative 24. Conversion of the co-carboxy group into the 9-fluorenylmethyl ester, followed by TFA treatment and reprotection of the M -amino group affords Boc-L-Asu(OFm)-OH (25). 

Pyridinium enolbetaines and cyclopropenones have been used as the three carbon atom components in a further illustration of type (ii) syntheses <71LA(746)102). The betaine is formed in situ by deprotonation of a pyridinium salt and good yields of the pyranone result simply on boiling in methanol solution. Considerable variation in the substituents is possible and triphenylphosphonium or diethylsulfonium enolbetaines may be used in place of the pyridinium compound. 

Alternatively it is possible to have both steps, addition and elimination, occur spontaneously if appropriate reagents are employed. There are two common strategies in use the Wittig reaction and the Wittig-Horner reaction. The Wittig olefination uses a phosphorus-stabilized carbanion (ylid) as a nucleophile and a carbonyl compound as an electrophile. Typically the ylid is generated in situ from a triphenylphosphonium salt and a strong base such as LDA or an alkyl lithium. 

We were able to direct the rearrangement 23—24 so that no disproportion into 9. and 30. occurred (13). The adducts 24 are stable and can now be used for hydroboration reactions whereby a suitable method for the elimination of triphenylphosphane from complex 24 must be used. This can be achieved with benzyl-iodide jjj. On a cIcTi-tion of the iodo compound 25 and an olefin 2 to a solution of 2 in tetrahydrofuran, the benzyl-triphenylphosphonium iodide precipitates and the free R-BH2 adds to the olefin 2 forming the tri-... 

This lipophilic cationic compound 267 has been synthesized410, as shown in equation 195, from / -iodoaniline via the triazene 268, reaction of the latter with triphenylphosphine and labelling the triphenylphosphonium iodide 269 with 125I. 267 is a potential agent for PDT (photodynamic therapy) for central nervous system malignancy411l-41 3. 

When 5,5-dimethyl-1,3-hexadiynyl(phenyl)iodonium triflate is mixed with two equivalents of triphenylphosphine in toluene, a mixture of bisphosphonium triflates is produced (equation 76)34. This transformation apparently involves the initial formation of (5,5-dimethyl-l,3-hexadiynyl)triphenylphosphonium triflate followed by competing Michael and conjugate Michael reactions of this compound with a second mole of triphenylphosphine. The ( -geometry about the carbon-carbon double bonds in both products has been established by NMR analysis34. 

The Wittig reaction is a C,C-forming olefin synthesis from phosphonium ylides and carbonyl compounds (see also Section 4.7.4). In more than 99% of all Wittig reactions, ylides of the structure Ph3P+—CH-—X (i.e., triphenylphosphonium ylides) are used. Therein, X usually stands for H, alkyl, aryl, or C02-alkyl and seldom for other substituents. 

A. S. Alves, D. S. Moore, R. A. Andersen, and G. Wilkinson, Triphenylphosphonium and Trimethylphosphonium Hexachloroosmates(IV) and Their Reactions with Alkylating Agents Methyl and Trimethylsilylmethyl Osmium Compounds tranj-Dichlorote-trakis(trimethylphosphine)osmium(II) Tetrakis(trimethylsilylmethyl)oxoosmium(VI), Polyhedron 1, 83-87 (1982). 

Tellurophene aldehydes and ketones readily undergo reduction reactions typical of carbonyl compounds. The Wittig reaction of 2,5-bis(dodecyloxy)- -xylene-bis(triphenylphosphonium bromide) with tellurophene-2,5-dicarbaldehyde leads to poly(2,5-tellurophenediylvinylene) (MW 7000-29000 Da) in 65% yield <1995MM8363>. The condensation reactions of 2,5-diphenyl-3,4-diformyltellurophene 15 have been employed for the synthesis of a number of bi- and polycyclic heterocycles with a fused tellurophene ring (Scheme 8) <1976CB3886>. 

More rational syntheses of related fiiran-containing systems involve the condensation of bis-ylides with bis-aldehydes. The simplest such approach involved the condensation of 2,5-diformylfiiran (169) with o-xylylene-bis[triphenylphosphonium bromide] (170) under basic conditions. The result was the production of three isomers of the formal 2 + 2 condensation product (Scheme 27) [146]. Irradiation of the three isomers 171-173 gave a single new isomer 174. Compound 174 may also be generated by the reaction of the bis-ylide 170 with 175 (Scheme 28) [147]. 

Fluorinated bromo or chloro compounds react with triphenylphosphane to fomn phosphonium salts. For example, 3-bromo-3.3-difluoroprop-l-ene (1) can be used to prepare (3,3-difluoro-allyl)triphenylphosphonium bromide (2), a useful reagent for the Wittig reaction. 

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