Phosphine triphenyl-, reduction

Reduction of amides is an important preparative method for the synthesis of primary amines. Reducing agents used for this purpose include lithium aluminum hydride, sodium borohydride, triphenyl-phosphine (Staudinger reduction), and thiols. In the present case it is important to consider the compatibility of the reduction system with the carboxylic and methanesulfonic acid functions. Platinum and palladium arc often used for catalytic reduction. 

The reduction of benzofuroxans can lead to a variety of products, depending upon the conditions. Deoxygenation to benzofurazans (40) can be effected either directly, using trialkyl phosphites, -tributyl or triphenyl - phosphine, or indirectly, via o-quinone dioximes (41), using methanol and potassium hydroxide, or hydroxyl-amine and alkali. - - The dioximes may be isolated, but... 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The Mitsunobu reaction was applied to the synthesis of pyrrolo[l,2-d [, 2,4]triazines from pyrrole derivative 71. Thus reduction of 71 gave alcohol 72, which on treatment with diethylazodicarboxylate and triphenyl phosphine gave 74 via the open chain intermediate 73. Hydrolysis of 74 gave 75 (84AG517) (Scheme 18). 

Recently, the electrolysis of aliphatic carboxylic acids in an undivided cell and in the presence of triphenyl phosphine has been reported, which turned out to be one of the most reliable methods for the reduction of aliphatic carboxylic acids to the corresponding aldehydes (Scheme 26) [11, 52]. In this reaction. 

Replacement of an allylic hydroxyl without saturation or a shift of the double bond was achieved by treatment of some allylic-type alcohols with triphenyliodophosphorane (PhjPHI), triphenyldiiodophosphorane (PhsPIj) or their mixture with triphenyl phosphine (yields 24-60%) [612]. Still another way is the treatment of an allylic alcohol with a pyridine-sulfur trioxide complex followed by reduction of the intermediate with lithium aluminum hydride in tetrahydrofuran (yields 6-98%) [67 J]. In this method saturation of the double bond has taken place in some instances [675]. 

Hydroxide attack on complexes of the type cis-[(NO)L(bpy)2Ru ] also yields the corresponding nitro complex [118]. The equilibrium constants for these reactions are a strong function of the cis-ligand and increased by 10 on changing L from a jr-donor (Cl ) to a rr-acceptor (py) [98]. The ability of the nitro complexes to transfer an oxygen atom to a reductant such as triphenyl-phosphine is also a function of the cis-ligand [98]. 

Thiols can be prepared by the reduction of sulfonyl halides652 with LiAIH4. Usually, the reaction is carried out on aromatic sulfonyl chlorides. Zinc and acetic acid, and HI. also give the reduction. Sulfonic acids have been reduced to thiols with a mixture of triphenyl-phosphine and either Ii or a diaryl disulfide.633 Disulfides RSSR can also be produced.634 For the reduction of sulfonyl chlorides to sulfinic acids, see 0-118. 

To avoid further oxidation of the aldehyde by the byproduct H2C>2 formed, hydrolysis is usually carried out in the presence of mild reducing agents.584,592 Catalytic hydrogenation, Zn + CH3COOH, and Nal or KI are the most frequently used conventional reductants.582 584 592 Dimethyl sulfide,622 triphenyl phosphine,607 and thiourea,623 introduced later, are likewise effective and selective reducing agents. 

For ageing experiments the toluene solution of the grafted polymer was first treated with an excess of triphenyl phosphine (reduction of residual hydroperoxides into alcohols), then suitable amount of the parent polymer was added and co-precipitation was performed into methanol. The polymer blend was vulcanized by adding dicumyl peroxide (5% w)prior precipitation (pressing conditions became 190°C, 190 bar, 5 min). 

Ullmann reaction (4, 33-34). Semmelhack et al.1 recorded details of the coupling of aryl and vinyl halides with Ni(0) complexes, (COD)2Ni or Ni[P(C6H5)3]4. This reaction was used for the first synthesis of almusone (3), an antileukemic lignan obtained from the wood of Alnus japonica Steud. In the case of ort/io-substituted aryl iodides such as 1, reduction becomes a competing reaction and the yields are only moderate. In fact o,o-disubstituted aryl halides cannot be coupled under these conditions. Deliberate addition of a proton source increases formation of the reduction product. Acetic or trifluoroacetic acid are useful for this purpose. Added triphenyl-phosphine also promotes reduction. 

Reductive aldol reaction of an allenic ester (52) to a ketone such as acetophenone can give y- (53-y) or a-product (53-cy).159 Using as catalysts a copper salt and a range of chiral phosphines, together with phosphine additives such as the triphenyl or tricy- clohexyl compounds, a highly selective set of outcomes can be achieved, e.g. (53-y) almost exclusively cis- with 99% ee, or - without additive - significant amounts of (53-a) can be formed (as a syn-anti mixture). A diastereoselective implementation of the latter has also been developed. 

Ozonoylsis followed by reductive workup with triphenyl phosphine produced aldehyde 2 which was subsequently oxidized to furnish the C-linked galactosyl pyranose derivative 3. 

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