Cyclizations iron chloride

Acenaphtheno[l,2-e][l,2,4]triazolo[4,3-h][l,2,4]triazine 747 was prepared (79AP147) by cyclizing 3-hydrazinoacenaphtheno[l,2-e][l,2,4]tria-zine 746 with formic acid. Reaction of 746 with sugars gave the hydrazones, which cyclized with iron(III) chloride to give 748 (93BCJ00). Similarly, the acetaldehyde derivative of 746 was cyclized to 748. The structure of 748 (R = Me) rather than 747 (R = Me) was deduced by unequivocal synthesis of the latter by condensation of acenaphthenequinone with 3,4-diamino[l,2,4]triazole (Scheme 155). 

Carboxylic acids, a-bromination of 55, 31 CARBOXYLIC ACID CHLORIDES, ketones from, 55, 122 CARBYLAMINE REACTION, 55, 96 Ceric ammonium nitrate [Ammonium hexa mtrocerate(IV)[, 55, 43 Chlorine, 55, 33, 35, 63 CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Cinnamomtnle, a-phenyl- [2-Propeneni-tnle 2,3-diphenyl-], 55, 92 Copper(l) iodide, 55, 105, 123, 124 Copper thiophenoxide [Benzenethiol, copper(I) salt], 55, 123 CYCLIZATION, free radical, 55, 57 CYCLOBUTADIENE, 55, 43 Cyclobutadieneiron tricarbonyl [Iron, tn-carbonyl(r)4-l,3-cyclo-butadiene)-], 55,43... 

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. 

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). 

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). 

In 1998, Oshima and coworkers ° reported few examples of radical cyclization mediated by Grignard reagents in the presence of iron(II) chloride (Scheme 57). However, this reaction often gives moderate yields. 

The benzimidoyl thiocarbodihydrazide (237) was cyclized by Soviet chemists to yield 3-phenyl-l,4-dihydro-l,2,4,5-triazine-6(5//)-thione (238). But since (237) was prepared by reaction of ethyl benzimidate and thiocarbodihydrazide this reaction can also be classified as a synthesis by a [5 + 1] atom fragment method (77KGS564). When the perfluoroalkyl hydrazidines (239) were heated with anhydrous iron(III) chloride, cyclization occurred with... 

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). 

The in situ synthesis of macrocyclic ligands by condensation of 2,6-diacetylpyridine with polyamines in the presence of metal ions represents one of the early demonstrations of the template effect . Curry and Busch reported the first penta-and hexadentate macrocycles (79 and 80)47), both of which are cyclized in the presence of iron(II) chloride tetrahydrate. The two ligands were isolated as highly... 

Condensed imidazoles are formed in excellent yield when aromatic nitro compounds, substituted in the ortho position with an N-heteroparaffinic substituent, are cyclized using various reducing agents such as metal oxalates, iron pentacarbonyl, triethylphos-phite,113 or titanous chloride.114 The same reaction takes place under... 

The best general procedure for preparing 2-substituted phenox-azines is the pyrolytic condensation of o-chloronitrobenzene derivatives with sodium o-bromophenolate,20,29 followed by reduction with stannous chloride or with iron filings in acetic acid and subsequent cyclization of the ether 10. If the ether 10 is previously A-formylated,... 

The chemistry of iron vinylidene complexes is dominated by the electrophilicity of the carbon atom adjacent to the iron organometallic unit. While addition of water leads to an acyl complex (i.e., the reverse of the dehydration shown in equation 10), addition of an alcohol leads to a vinyl ether complex. Similarly, other iron vinyl complexes can be prepared by the addition of thiolate, hydride, or an organocuprate (Scheme 33). " The nucleophilic addition of imines gave enaminoiron intermediates that could be further elaborated into cyclic aminocarbenes. This methodology has been used to provide access to /3-lactams and ultimately penicillin analogs, and good diastereoselectivities were observed (6 1-15 1) (Scheme 34). 04 Iso, vinylidene complexes are intermediates in cyclizations of alkynyl irons with substituted ketenes, acid chlorides, and related electrophiles an example is shown (equation 11). These cyclizations led to the formation of a series of isolable and characterizable cyclic vinyl iron complexes. 

Quinoxalin-2-amine (14) can be synthesized by intramolecular cyclization of (2-aminophcnyl)-aminoacetonitrile (13) to form 3,4-dihydroquinoxalin-2-amine which is then dehydrogenated. The 3.4-dihydroquinoxalin-2-amine need not be isolated for conversion to quinoxalin-2-amine (14). since addition of hydrogen peroxide to the mixture in the presence of a catalytic amount of a transfer agent, such as iron(II) chloride, brings about the required dehydrogenation. ... 

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. 

Cyclization using palladium on charcoal in nitrobenzene at reflux can be used instead of iron(III) chloride to give a 34% yield of 8-aminophenazine-2-carbonitrile. ... 

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