Oxidative cyclization manganese® acetate

The carbazole-1,4-quinol alkaloids are also accessible by the iron-mediated arylamine cyclization (Scheme 14). Electrophilic substitution reaction of the arylamine 24 with the complex salts 6a and 6b affords the iron complexes 25. Protection to the acetates 26 and oxidative cyclization with very active manganese dioxide leads to the carbazoles 27, which are oxidized to the carbazole-... 

Palladium acetate has also been used to catalyze oxidative cyclizations to produce the related dihydroindole in dimethylacetamide (DMA) in moderate yields <1997BMEL749> (Equation 68). Similar cyclizations have been reported to occur in the presence of manganese dioxide and nitrobenzoic acid <1997TL7207>. 

In those cases where a hydroxyethyl substituent is attached to the cyclohexadiene ting, an oxidative cyclization procedure has been developed to effect conversion to cyclohexadienyliron complexes.14 Thus, treatment of complex (52) with manganese dioxide gives the cyclic ether (53) which can be converted to the dienyl complex (54 Scheme 7) by treatment with tetrafluoroboric acid in acetic anhydride. 

The manganese(UI) acetate mediated oxidative cyclization of fl-ketoesters has been utilized to construct a pentacyclic compound in low yield [95CC403]. The intermediate radical 107 formed from an initial 6-endo-trig reaction undergoes further lactonization in the presence of copper(II) acetate. The compound 108 has the basic skeleton found in fungal metabolite sesquiterpene phenols. 

A combination of radical and electron transfer steps mediated by manganese triacetate has been used in the synthesis of 5-acetoxyfuranones 21 through carbox-ymethyl radical addition to mono- and disubstituted alkynes 20, followed by oxidative cyclization of the resulting vinyl radicals 22 (Scheme 2.4). The cyclic intermediate 24 is transformed into the furanone 21 through stepwise one-electron oxidation and capture of the resulting aUyl cation 26 by acetate. 

Mohrle and Gundlach - carried out the oxidative cyclization of the 2-aminobenzylamines 267 with the mercuric acetate-EDTA reagent to obtain the nitrogen bridgehead compounds 270 in 64-80% yields. The oxidation of the tricyclic compounds 270 with manganese dioxide produced the corresponding fused quinazolinones 99. ... 

Oxidative cyclization Cupric chloride. Manganese dioxide. Mercuric acetate. 

Manganese(III)-mediated radical reactions have become a valuable method for the formation of carbon-carbon bonds over the past thirty years since the oxidative addition of acetic acid (1) to alkenes to give y-butyrolactones 6 (Scheme 1) was first reported by Heiba and Dessau [1] and Bush and Finkbeiner [2] in 1968. This method differs from most radical reactions in that it is carried out under oxidative, rather than reductive, conditions leading to more highly functionalized products from simple precursors. Mn(III)-based oxidative free-radical cyclizations have been extensively developed since they were first reported in 1984-1985 [3-5] and extended to tandem, triple and quadruple cyclizations. Since these additions and cyclizations have been exhaustively reviewed recently [6-11], this chapter will present an overview with an emphasis on the recent literature. 

Palladium(0)-catalyzed coupling of iodobenzene (153) and the commercial arylamine 154 afforded quantitatively the diarylamine 156 (Scheme 34) [178]. The oxidative cyclization of the diarylamine 156 to clausine L (148) is catalytic in palladium(II) and copper(II) acetate (or manganese(lll) acetate, respectively). Thus, air is the actual oxidizing agent in this process. For example, employing only... 

Yet another efficient synthesis of evodiamine and rutaecarpine has been reported. This latest one involves the oxidative cyclization of the tetracyclic amide (29) by means of mercuric acetate, which gave ( )-evodiamine (30) in 92% yield (Scheme 5). Oxidation of evodiamine with active manganese dioxide then completed the synthesis of rutaecarpine (26). 

Oxidative radical cyclization sequences have also been used to generate 1,2-fused indoles. Treatment of amides 152 and 154 with dimethyl methylmalonate in the presence of manganese(III) acetate and sodium acetate in acetic acid, gave the expected cyclized product in 63% and 40%, respectively [97]. The proposed mechanistic sequence involves the intermolecular addition of the dimethyl methylmalonate radical to the tethered exocyclic alkene followed by cyclization and finally rearomatization. Byers and coworkers also achieved a similar cyclization on the C-2 position of the indole when a 3-acylindole was subjected to these oxidative cyclization conditions. 

Among the oxidants that have been used to generate radicals, manganese (HI) acetate has emerged as a powerful reagent to mediate radical cyclizations.147 The manganese(III) acetate-mediated oxidation of enolizable carbonyl compounds is one of the best methods available for the cyclization of electrophilic radicals. The substrates are vety easily prepared by standard alkylation and acylation reactions. Radicals are formed with high selectivity by oxidation of acidic C—H bonds, and, because the reaction is an oxi-... 

Hwu et al. have examined the dependence of the metal oxidant on the mode of reactivity in silicon-controlled allylation of 1,3-dioxo compounds [95JOC856]. The use of manganese(III) acetate furnished the dihydrofuran product 22 only. On the other hand, use of cerium(IV) nitrate resulted in the formation of both acyclic (23) as well as the cyclized compound, with the product distribution dependent on the nature of the allylsilane. Facile synthesis of dihydrofurans by the cerium(IV) mediated oxidative addition of 1,3-dicarbonyl compounds to cyclic and acyclic alkenes has also been reported [95JCS(P1)187]. 

Reactions of 2,4-pentanedione or ethyl acetoacetate with ethene in the presence of manganese(III) acetate and copper(II) acetate in an autoclave under 50 atm at 60 °C give a mixture of 443 and 444 (equation 150). This reaction involves an oxidative 1,3-cyclization of alkyl radicals . 

Oxidations of 2,2 -diaminobiphenyls with sodium perborate, phenyl iodosodiacetate, ° or manganese dioxide have given benzo[c]cinnolines with hydrogen peroxide in acetic acid, cyclization is accompanied by N-oxidation. These reactions, which parallel the oxidation of arylamines... 

Routes via o-aminophenylpyrroles present the most convenient syntheses of a wide variety of pyrrolo[l,2-a]quinoxalines. Thus reaction of the amino compound 6 with acetic anhydride in acetic acid gave the acetamido derivative which was cyclized with phosphoryl chloride to give the 4-methyl compound 7 (R = Me) in 56% yield. The 4-phenyl compound 7 (R = Ph) has been prepared similarly. An even more convenient synthesis of 4-aryl compounds is achieved by reaction of compound 6 with aromatic aldehydes to give the 4,5-dihydro derivatives These are readily oxidized to 4-arylpyrrolo[l,2-a]quinoxalines 9 with manganese dioxide. This approach may be carried out in one step by reaction of compound 6 with aromatic aldehydes (e.g., benzaldehyde) in the presence of cupric acetate. Reaction of the aminophenylpyrrole 6 with 90% formic acid gave pyrrolo[l,2-a]quinoxaline (7, R = H) directly in 98% yield. Pyrrolo[l,2-a]quinoxalines substituted in the l-position and the 7-position have also been prepared from appropriately substituted... 

B-Keto-esters containing an alkene will undergo a manganese(III) oxidation reaction resulting in ring closure as shown in the reaction of (91). However other examples proceed in poor yield only. a,w-Bis-allylie acetates such as (92) undergo a palla-dium(0)-induced reductive cyclization in the presence of hexa-... 

Snider BB, Merritt JE, Dombroski MA, Buckman, BO. Solvent effects on manganese(III)-based oxidative free-radical cyclizations ethanol and acetic acid. J. Org. Chem. 1991 56 (19) 5544-5553. 

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