With triphenylphosphine

The high nucleophilicity of sulfur atoms is preserved, even if it is bound to electron withdrawing carbonyl groups. Thiocarboxylales, for example, substitute bromine, e.g. of a-bromo ketones. In the presence of bases the or-acylthio ketones deprotonate and rearrange to episulfides. After desulfurization with triphenylphosphine, 1,3-diketones are formed in good yield. Thiolactams react in the same way, and A. Eschenmoser (1970) has used this sequence in his vitamin B]2 synthesis (p. 261). 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

The physical properties of low melting point (60—105°C) syndiotactic polybutadienes commercially available from JSR are shown in Table 1. The modulus, tensile strength, hardness, and impact strength all increase with melting point. These properties are typical of the polymer made with a cobalt catalyst modified with triphenylphosphine ligand. 

A number of reductive procedures have found general applicability. a-Azidoketones may be reduced catalytically to the dihydropyrazines (80OPP265) and a direct conversion of a-azidoketones to pyrazines by treatment with triphenylphosphine in benzene (Scheme 55) has been reported to proceed in moderate to good yields (69LA(727)23l). Similarly, a-nitroketones may be reduced to the a-aminoketones which dimerize spontaneously (69USP3453279). The products from this reaction are pyrazines and piperazines and an intermolecular redox reaction between the initially formed dihydropyrazines may explain their formation. Normally, if the reaction is carried out in aqueous acetic acid the pyrazine predominates, but in less polar solvents over-reduction results in extensive piperazine formation. 

This group, which is more stable than the 2-hitrobenzenesulfenamide, has been developed to protect amino acids. It is readily introduced with the sulfenyl chloride (52-74% yield) and is cleaved with triphenylphosphine or 2-thiopyridine N-oxide. It is stable to CF3COOH but can be cleaved with 0.1 M HCl. ... 

The conversion of coordinated NSCI into a nitrido ligand provides a useful synthesis of transition-metal nitrides. For example, treatment of ReCl4(NSCl)(POCl3) with triphenylphosphine generates the nitrido complex ReNClaCPPhsla. "... 

Only a few reactions of benzodithiadiazines have been investigated. In common with dithiatriazines 12.8, the anti-aromatic system 12.12 (R = H) undergoes a reversible 5,5 -cycloaddition with norbornadiene. The reaction of 12.12 (R = F) with triphenylphosphine results in a ring contraction to give the imino 2 -phosphane 12.13. ... 

Wipf and Miller have reported side-chain oxidation of 3-hydroxy amides with the Dess-Martin periodinane, followed by immediate cyclodehydration with triphenylphosphine-iodine, which provides a versatile extension of the Robinson-Gabriel method to substituted oxazoles. Application of this method was used to prepare the oxazole fragment 10 in 55% overall yield from 3-hydroxy amide 8. 

Complex 105 enters the pyrazoleAriphenylphosphine ligand substitution reaction with PPha to give 108 (910M3123). Further reaction with triphenylphosphine and silver tetrafluoroborate gives the heterodinuclear complex 109 (94IC2196). 

The N-coordinated compound [AuCljL] (L= l-ethyl-2-phenylimidazole) with silver tetrafluoroborate gives the cycloaurated species 102, which on further reaction with triphenylphosphine and sodium tetrafluoroborate or ammonium hexafluorophosphate forms the cationic complexes 103 (X = BF., PF,) (00JCS(D)271). 

Interaction of the latter with triphenylphosphine in the presence of sodium perchlorate leads to the cationic complex [(dppm)Au2(li-L)Pd(C Fj)(PPh3)]C10. Reactions of [L Au(p-L)AuL ] (L = bibenzimidazolate L = PPh, dppm)] with [Pd(0C103)(C Fj)(PPh3)2] do not lead to the tetranuclear products. Only the bibenzimidazolate (L) dinuclear product [(PPh3)(C F3)Pd(p-L)Pd(C, F3)(PPh3)] could be isolated in both cases. 

The reaction of cyclopropyl bromide with triphenylphosphine gives the expected phosphonium salt in less than 1 % yield. An alternate route to the salt by the thermal decomposition of 2-oxo-3-tetrahydrofuranyltriphenylphosphonium bromide gives a... 

Figure 4.1-13 Comparison of the experimental without (—) and with (—) triphenylphosphine at (solid line) and fitted (dashed line) (a) EXAFS 80 °C and in the presence of triphenylphosphine and (b) pseudo-radial distribution functions and reagents at 50 °C for 20 min (—). Repro-...

An aldehyde or ketone reacts with a phosphorus ylide to yield an alkene in which the oxygen atom of the carbonyl reactant is replaced by the =0 2 of the ylide. Preparation of the phosphorus ylide itself usually involves reaction of a primary alkyl halide with triphenylphosphine, so the ylide is typically primary, RCH = P Ph)3-This means that the disubstituted alkene carbon in the product comes from the carbonyl reactant, while the monosubstituted alkene carbon comes from the ylicle. 

Scheme 3b). It is instructive at this point to reiterate that the furan nucleus can be used in synthesis as a progenitor for a 1,4-dicarbonyl. Whereas the action of aqueous acid on a furan is known to provide direct access to a 1,4-dicarbonyl compound, exposure of a furan to an alcohol and an acid catalyst should result in the formation of a 1,4-diketal. Indeed, when a solution of intermediate 15 in benzene is treated with excess ethylene glycol, a catalytic amount of / ara-toluenesulfonic acid, and a trace of hydroquinone at reflux, bisethylene ketal 14 is formed in a yield of 71 %. The azeotropic removal of water provides a driving force for the ketalization reaction, and the presence of a trace of hydroquinone suppresses the formation of polymeric material. Through a Finkelstein reaction,14 the action of sodium iodide on primary bromide 14 results in the formation of primary iodide 23, a substance which is then treated, in crude form, with triphenylphosphine to give crystalline phosphonium iodide 24 in a yield of 93 % from 14.

Unsaturated -lactone 34 adopts a well-defined conformation and provides a suitable platform for the introduction of the stereogenic center at C-24 (monensin numbering). Catalytic hydrogenation of the carbon-carbon double bond in 34 takes place preferentially from the less hindered side of the molecule and provides an 8 1 mixture of stereoisomers in favor of 35 (100% yield). Cleavage of -lactone 35 with concentrated hydriodic acid at 130°C, followed by treatment of the resultant iodide 36 with triphenylphosphine, completes the synthesis of intermediate 19. 

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