Oxidative cyclization iron chloride

An attempt to directly convert hyellazole (245) to 6-chlorohyellazole (246) by reaction with N-chlorosuccinimide in the presence of a catalytic amount of hydrochloric acid led exclusively to 4-chlorohyellazole. On the other hand, bromination of 245 using NBS and a catalytic amount of hydrobromic acid gave only the expected 6-bromohyellazole (733). Alternatively, a direct one-pot transformation of the iron complex 725 to 6-bromohyellazole (733) was achieved by reaction with an excess of NBS and switching from oxidative cyclization conditions (basic reaction medium) to electrophilic substitution conditions (acidic reaction medium). Finally, a halogen exchange reaction with 4 equivalents of cuprous chloride in N,N-dimethylformamide (DMF) at reflux, transformed 6-bromohyellazole (733) into 6-chlorohyellazole (246) (602) (Scheme 5.73). 

The 1,2,4-triazole ring of 267 was formed by oxidative cyclization of aldehydo-sugar lepidin-2-yl-hydrazones (266) with iron(III) chloride (94MI6) (Scheme 80). 

Oxidative cyclization of 2 with lead tetraacetate (57JCS727 71GEP-2004713) or with ethanolic iron (III) chloride [94JCR(S)412] afforded the respective 3-substituted l,2,4-triazolo[4,3-c]pyrimidines 3 (Scheme 5). 

Hydrazone 69 (R = H) derived from 3-hydrazino-5//-l,2,4-triazino[5,6-6]indole (67, R = H) and aldose monosaccharides (68) produced the acyclo C-nucleoside (70, R = H) upon oxidative cyclization with iron(III) chloride (92BCJ546). The poly-O-acetyl derivatives of the 10-methyl and 10-ethyl congeners (70, R = Me or Et) were obtained in one step from the corresponding hydrazones (69, R = Me or Et) by cyclization with a mixture of bromine in acetic acid, anhydrous sodium acetate, and acetic anhydride (97UP1) (Scheme 22). 

The acyclic C-nucleoside analogues of 1,3,4-thiadiazoles 247 were prepared by the oxidative cyclization of the thiosemicarbazones 248 (X = S) with iron(III) chloride (86JPR1 87BCJ3405). The respective oxadiazole analogues were prepared by the oxidation of the acetate of 248 (X = O) with iodine (72MI1). Both of the aroylhydrazones and thiosemicarbazones... 

The structure of 2-anilino-5-phenylazo-1,3,4-thiadiazole (89 R = Ph) is established by its alternative synthesis from 2-amino-5-anilino-l,3,4-thiadiazole (90) and nitrosobenzene by the Mills reaction. Further examples of arylazo-thiadiazoles of this type (89) have been prepared by the oxidative cyclization of l-aryl-5-arylthiocarbamoylthiocarbonohydrazides (e.g. p-TolNHNH-CS-NHNH-CS-NHR, i.e. bithiourea derivatives), using bromine, hydrogen peroxide, or aqueous iron(iii) chloride as oxidizing agent. ... 

As for the oxidative cyclization that uses iron(III) chloride, to effectively suppress the polymerization, the DDQ/acid-mediated variant of the SchoU reaction requires the blocking of the a positions of thiophene rings. 

Tricarbonyl(cyclohexadienyl)iron cations react with a variety of nucleophiles to give substituted tricarbonyl(cyclohexadienyl)iron complexes88 with arylamines, N- or C-alkylation can occur depending on the nature of aryl ring substituents. Deligation of C-alkylated arylamines can be achieved by either ferric chloride, which gives the free arylamine, or by iodine in the latter case, cyclization with concomitant oxidation occurs, and carbazoles are produced in moderate yield (Scheme 52).89... 

Oxidation may be achieved in the presence of oxygen or air. Other suitable oxidants include sulfur, sodium polysulfide, iron (III) chloride, potassium ferro-cyanide (III) or potassium dichromate, peroxydisulfate or salts of aromatic nitro-sulfonic acids. An aqueous/alkaline medium is used in the presence of a high boiling organic solvent which is not miscible with water or which is almost immiscible with water. Cyclization with chlorosulfonic acid can be followed directly by oxidation with bromine to afford the thioindigo system, without separation of the intermediate. 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

Iron(iii) chloride has been used as an oxidant to catalyze the cyclization of acyclic precursors to highly derivatized benzodithiophenes <2006TL1551>. Thus, thiophene-based polycyclic aromatics have been produced in high yield (Equation 75). 

Synthetically useful routes to dibenzo[c,e J[l,2]dithiins are normally based on cyclizations of biphenyI-2,2 -disulfonyl chlorides. A method applied successfully to the parent compound reduces the precursor with zinc in acetic acid to generate the bis thiol, which is then gently oxidized to the dithiin using iron(II) chloride (66HC(21-2)952). An alternative one-step reductive cyclization, which has been applied to the preparation of the 2,9- and 3,8-dinitro derivatives, involves reduction of the appropriate bis sulfonyl chlorides with hydriodic acid in acetic acid (68MI22600). Yet another reductive cyclization uses sodium sulfite followed by acidification, and these conditions lead to dibenzo[c,e][1,2]dithiin 5,5-dioxide. The first step of the reaction is reduction to the disodium salt of biphenyl-2,2 -disulfinic acid which, on acidification, forms the anhydride, i.e. dibenzo[c,e][l,2]dithiin 5,5,6-trioxide. This is not isolated, but is reduced by the medium to the 5,5-dioxide (77JOC3265). Derivatives of dibenzo[c,e] [1,2]dithiin in oxidation states other than those mentioned here are obtainable by appropriate oxidation or reduction reactions (see Section 2.26.3.1.4). 

When both benzene rings are amino-substituted in the ortho positions, phenazines are easily formed in good yield with the elimination of an ortho group. Reaction of 2,2 -diaminodiphenyl-amines 3 with iron(III) chloride in dilute hydrochloric acid affords initially, by a cyclization reaction with concomitant elimination of ammonia, dihydrophenazines which undergo rapid oxidation in air to the corresponding phenazines 4 in almost quantitative yields. 

Related reactions include the formation of the 2-cyano compounds (190) when 1,2-dimethyl-5-nitroimidazole is heated with nitrosyl chloride or an AT-oxide, and when 2-methyl-l-(o-nitrophenyl)imidazoles (191) cyclize under the influence of iron(II) oxalate (Scheme 98) (74JCS(P1)1970). The last reaction product is contaminated by a large amount of amine reduction product ( 64%) but there is also some cyclization with the 4-methyl isomer of (191). In the presence of trimethylamine, 2-cyanomethylbenzimidazole condenses with acetone to give the unsaturated derivative (192 Scheme 99) (77CPB3087). Neither 2-methylimidazole nor 2-methylbenzimidazole reacts with formamide in the presence of phosphoryl chloride. 

The Pictet-Spengler cyclization of )VA -dimethyltryptamine (V-oxide (66) to the tetrahydrocarboline (78) using sulfur dioxide in anhydrous formic acid and the selective (V-dealkylation of the morphinan iV-oxide (79) using catalytic quantities of iron(II) chloride (equations 19 and 20) illustrate the advantages of using these activating reagents in the Polonovski reaction. 

Iron nitrate supported on bentonite induces the sequential oxidation of benzyl alcohols, and Prins cyclization of the aldehydes formed, with homoallylic alcohols and trimethylsilyl chloride to provide 2-aryl-4-chlo-rotetrahydro-2Ef-pyrans (Scheme 15) (13SL1781). 

Methylene blue is formed from dimethyl-p-phenylenediamine, with an indammonium salt (Bindschedler s green) as an intermediate this condenses with hydrogen sulphide giving the thiazine dye (Fig. 5-1). Iron(//f) chloride is the usual oxidant for the condensation and cyclization reactions, but iron(//7) sulphate or oxalate may be used instead. The colour intensity of the dye is pH dependent. According to Cline (1969) the optimum pH is 0.35. 

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