Oxidative coupling Potassium ferricyanide

Since the mid-1950s, phenol oxidative coupling (7) has been actively applied to the synthesis of many types of alkaloids, with considerable progress being achieved especially in the field of isoquinoline alkaloids (8-H). As to aporphine synthesis, employment of new reagents such as vanadium oxyfluoride (12) greatly improved yields as compared to classical methods such as oxidation with potassium ferricyanide and ferric chloride. 

There are many reports on the biogenetic synthesis of these alkaloids by phenol oxidation. These reactions were carried out using a diphenolic isoquinoline with one-electron oxidizing reagents ferric chloride, potassium ferricyanide, manganese dioxide, and so on. In order to obtain the androcymbine-type compound 82 the diphenolic isoquinoline 81 was subjected to phenol oxidation with potassium ferricyanide (3a) and with ferric chloride (2b), respectively, but instead the homo-aporphine 83 (2a) coupled at the ortho-ortho position to the hydroxy groups. 

A synthesis of ( + )-cularine (61) (mp 119°) by oxidative coupling of the diphenolic benzylisoquinoline (59) has been achieved. The oxidant was potassium ferricyanide in a two-phase system (8% ammonium acetate-chloroform) and gave the phenolic product (60) (mp 126°) in 7% yield. Methylation with diazomethane completed the synthesis. The compound 59 was prepared as its dibenzyl derivative by a mild variant of the Pomerantz-Fritsch synthesis 76). 

A new development is that electrochemical oxidation of ferrocyanide to ferricyanide can be coupled with AD to give a very efficient electrocatalytic process [37]. Under these conditions, the amount of potassium ferricyanide needed for the reaction becomes catalytic and Eqs. 6D.6 and 7 can be added following Eq. 6D.4. Summation of Eq. 6D.1-6D.4, 6D.6, and 6D.7 gives 6D.8, showing that only water in addition to electricity is needed for the conversion of olefins to asymmetric diols and that hydrogen gas, released at the cathode, is the only byproduct of this process. In practice, sodium ferrocyanide is used in the reaction and the amount of this reagent used in comparison with the potassium ferricyanide method mentioned above has been reduced from 3.0 equiv. to 0.15 equiv. (relative to an equivalent of olefin). 

The ring system of the homoerythrina alkaloids has been prepared (149) by oxidative coupling of the 1-phenethyltetrahydroisoquinoline (206, R = COCF3) (Scheme 44). The diphenol (208) was obtained in 76% yield from 207, but all attempts to oxidize the A-trifluoroacetate of 208 to a dipheno-quinone failed—probably because the two aromatic rings are orthogonal to each other. However, oxidation of the secondary amine (208) itself with potassium ferricyanide gave a mixture of 209 (45% yield) and 210 (15%) ... 

The pioneer in phenolate radical coupling was Pummerer. In 1925 he showed1 that one electron oxidation of />-cresol using potassium ferricyanide afforded a nicely crystalline ketonic dimer of the radical in up to 25 % yield. Pummerer s ketone, as it became known, was considered to result from the coupling of two p-cresol radicals to give the dienone 1. This then underwent spontaneous cyclization to furnish 2. As proof of the structure... 

Hiinig and Oette prepared azothiadiazoles (85) by oxidative coupling of 3-methyl-l,3,4-thiadiazolin-2(3)-one hydrazones (84) with phenols and diphenylamine. 84 was prepared by reaction of 2-methyl-thio-3-methyl-l,3,4-thiadiazolium ions (82) with benzhydrazide and hydrolysis of the first formed benzhydrazone (83). The coupling to 85 was performed with potassium ferricyanide in alkaline medium. 

PhenoUc oxidative coupling. Oxidation of the secondary amine (I) with potassium ferricyanide in the presence of sodium hydrogen carbonate in chloroform gives the dienone (2, norerylhrinadienone). ... 

OXIDATIVE COUPLING Cuprous chloride. Ferric chloride-Dimethylformamide. Manganese dioxide. Palladium(ll) chloride. Potassium ferricyanide. Silver carbonate-Celite. Thallium(Ill) trifluoroacetate. 

Two studies have appeared dealing with the phenolic oxidative coupling of the dihydric benzylisoquinoline LI. In the first study, oxidation of LI with potassium ferricyanide yielded two dienones (LII), one of which was obtained crystalline. The crystalline material was reduced with sodium borohydride to two noncrystalline dienols (LIII) which underwent dienol-benzene rearrangement in anhydrous methan-olic hydrogen chloride to ( )-corydine (XXVI). Rearrangement of the... 

In recent work Kende and his coworkers have explored intramolecular oxidative coupling between phenolate and enolate, rather than between two phenolates. This proved a viable process for certain carbonyl enolates, and for nitro-stabilized anions, llius potassium ferricyanide oxidations of the indandione... 

Lunarine (26), one of the typical neolignans, is biosynthesized by the ortho-para radical coupling between two molecules of p-hydroxycinnamic acid. In this connection, oxidative coupling reactions of 4-substituted phenols have been extensively stndied using thallium trifluoroacetate (TTFA), potassium ferricyanide (K3[Fe(CN)g]) and other reagents. p-Cresol (27) was also electrolyzed at a controlled potential (+0.25 V vi. SCE) in a basic medium to afford Pummerer s ketone 28 in 74% yield. The snggested mechanism is given in Scheme 4. 

The existence of homoerythrina alkaloids has been anticipated from biosynthetic considerations. Homoerythrina dienone 77 was synthesized in the following way. Oxidation of the diphenolic isoquinoline 86 with vanadium oxytrichloride in methylene chloride afforded the expected prohomoerythrinadienone 87 (47), which was transformed to the imine 88 in quantitative yield by 1 N sodium hydroxide at 0°C. Sodium borohydride reduction of the iminium chloride of 88 gave 76. Oxidative phenolic coupling of 76 with potassium hexacyanoferrate in methylene chloride afforded homoerythrina dienone 77 in 45% yield and homoery-sodienone 89a in 15% yield (48). Moreover, the lactam dienone 91 was prepared in excellent yield by oxidation of the N-acyltetrahydroquinoline 90 with potassium ferricyanide (49). 

Chen and Liu (1977) utilized the spontaneous oxidation of NADH by potassium ferricyanide for the construction of a potentiometric LDH electrode. The coupled reduction of ferricyanide ions to ferrocyanide ions results in a measurable electrochemical zero-current potential. The potential was found to be Nemstian in nature and directly proportional to the logarithm values of lactate concentration over the range 0.02 to 50 mmol/1. The response time was as high as 10 min. 

The Amaryllidaceae alkaloids2 probably arise by intramolecular oxidative phenol coupling. Indeed Barton3 has effected a synthesis of ( )-narwedine (4) by oxidation of (3) with potassium ferricyanide however, the yield of (4) was only... 

Suitably (lydroxylated benzophenones are oxidatively coupled to give xan> thones by manganese dioxide, DDQ or potassium ferricyanide [2151, 2941]. 2 -Halo-2-hydroxybenzophenones, which are capable of forming benzyne intermediates, are converted into xanthenones by potassamide. Some 3 -halo-2-hydroxybenzophenones also yield xanthenones as one of several products [2676]. 

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