Alkenes, with acids phosphites

A range of aromatic alkenes and acrylic acid derivatives have been converted into benzyl alcohols and a-hydroxyalkanoic acids in good yields by a reductive oxidation process. This reaction is accomplished by reaction with oxygen and triethylsilane with a cobalt(II) catalyst, followed by treatment with trialkyl phosphites (equation 30)154. The aromatic olefins may also be converted into the corresponding acetophenone in a modified procedure where the trialkyl phosphite is removed155. In a similar reaction 2,4-alkadienoic acids are converted into 4-oxo-2-alkenoic acids156. 

Water-soluble palladium(O) complexes have also been used as homogeneous catalysts in aqueous-solution alkylation reactions. The particular complex that has been used is Pd(TPPMS>3. Aryl or heteroaromatic halides can be coupled with aryl or vinyl boronic acids, alkynes, alkenes, or dialkyl phosphites with this palladium(0) complex. This complex in aqueous solution can also be used for the coupling of alkynes with unprotected iodonucleotides, iodonucleosides, and iodoamino acids (133). 

The success of simple Au(I) PPhj systems for catalysis inspired the development of less strongly donating phosphine hgands in order to enhance it-acidity to improve reactivity with protected amines. Using triphenyl phosphite as a hgand, intermolecular hydroamination of alkenes with sulfonamides can be accomphshed with low catalyst loadings (Scheme 15.63) [263]. 

When Ni(LL)(Me4-l,4-benzoquinone), where LL = a bidentate cyclic alkene such as cot, cod, nor, or en /o-dicyclopentadiene, reacts with trimethyl phosphite, it is the alkene LL which is replaced first, en route to the product Ni(P OMe 3)4. This first step is bimolecular, producing an intermediate containing unidentate alkene. Some kinetic parameters are reported, particularly for LL = cyclo-octa-1,5-diene. The formation of the cation [NiH(P OEt 3)4]+ in perchloric acid-methanol solution appears to involve direct protonation of the nickel. Activation parameters for this are = 13 1 kcalmoL and AS = — 2 3 cal deg mol . 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

Attack on Unsaturated Carbon. The annual addition of phosphites to every variety of activated double bond continues. These include nitro-alkenes,9 a/S-unsaturated carboxylic acid derivatives,10 maleimides,11 fulvenes,12 and pyridinium salts.13 The reaction of diethyl phosphite with keten 0,N-, S,N, and Al,AT-acetals has been used to prepare the enamine phosphonates (19).14... 

Of trialkyl phosphites the most frequently used is triethyl phosphite (EtO)3P (M.W. 166.16, b.p. 156°, density 0.969) which combines with sulfur in thiiranes [291, 294] and gives alkenes in respectable yields. In addition, it can extrude sulfur from sulfides [295], convert a-diketones to acyloins [296], convert a-keto acids to a-hydroxy acids [297], and reduce nitroso compounds to hydroxylamines [298] Procedure 47, p. 111). 

Doubly acceptor-activated imines with an intramolecular alkene moiety such as 29 can cyclize according to an electrophilic mechanism to give pyrrolidine, piperidine or azepine derivatives. This reaction is induced by stoichiometric amounts of Lewis acids, preferably trialkylsilyl triflates [38]. In certain cases FeCl3 can also be used, for example for the preparation of azepinolactone 30 from imine 29 (Scheme 8.10) [39]. Catalytic amounts of FeCl3 are required for the addition of diethyl phosphite to an... 

Hydrocyanation is the formal addition of hydrogen cyanide to alkenes. alkynes, and dienes to yield nitriles. These reactions can be catalyzed by various copper, cobalt, nickel and palladium catalysts modified with phosphanes and phosphites and/or Lewis acids. Hydrocyanation of carbonyl groups in aldehydes and ketones is covered in Section D.l.3.7. 

Lewis acid catalyzed versions of [4 4- 2] cycloadditions are restricted to functionalized dieno-philes. Nonfunetionalized alkenes and alkynes cannot be activated with Lewis acids and in thermal [4 + 2] cycloadditions these suhstrates usually show low reactivity. It has been reported that intcrmolecular cycloaddition of unactivated alkynes to dienes can be accelerated with low-va-lent titanium, iron or rhodium catalysts via metal-mediated - -complex formation and subsequent reductive elimination39 44. Usually, however, low product selectivities are observed due to side reactions, such as aromatization, isomerization or oligomerization. More effective are nickel-catalyzed intramolecular [4 4- 2]-dienyne cycloadditions which were developed for the synthesis of polycycles containing 1.4-cyclohexadienes45. Thus, treatment of dienyne 1, derived from sorbic acid, with 10mol% of Ni(cod)2 and 30 mol % of tris(o-biphenyl) phosphite in tetrahydrofuran at room temperature affords bicyclic 1,4-dienes 2, via intramolecular [4 + 2] cycloaddition, with excellent yield and moderate to complete diastereocontrol by substituents attached to the substrate. The reaction is sensitive towards variation in the catalyst and the ligand. 

ANHYDRONE (10034-81-8) A powerful oxidizer. Potentially violent or explosive reaction with reducing agents, alcohols, ammonia gas, argon (wet), butyl fluorides, dimethyl sulfoxide, ethylene oxide, fluorobutane (wet), fuels, hydrazines, hydrocarbons, mineral acids, powdered metals, organic matter, phosphorus, trimethyl phosphite. Mixture with ethanol forms explosive ethyl perchlorate. Incompatible with alkenes, and many other materials. Shock may cause magnesium perchlorate to explode. 

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