Cyclization agents/cyclizations

CgH,oN20. Colourless crystalline solid, m.p. 121 °C. Made by reacting phenylhydrazine with ethyl acrylate to obtain the hydrazide which cyclizes to the product. Its major commercial importance is as a photographic developing agent, being used particularly in conjunction with hydroquinone. 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Scheme 98) (523). Hydrogen chloride is unsatisfactory as a cyclizing agent, whereas hydrogen iodide causes further reduction and leads directly to derivatives of the previously inaccessible 4-aminothiazoles (see Section VII. 2). 

DiaUyl fumarate polymerizes much more rapidly than diaUyl maleate. Because of its moderate reactivity, DAM is favored as a cross-linking and branching agent with some vinyl-type monomers (1). Cyclization from homopolymerizations in different concentrations in benzene has been investigated (91). DiaUyl itaconate and several other polyfunctional aUyl—vinyl monomers are available. 

Conra.d-Limpa.ch-KnorrSynthesis. When a P-keto ester is the carbonyl component of these pathways, two products are possible, and the regiochemistry can be optimized. Aniline reacts with ethyl acetoacetate below 100°C to form 3-anilinocrotonate (14), which is converted to 4-hydroxy-2-methylquinoline [607-67-0] by placing it in a preheated environment at 250°C. If the initial reaction takes place at 160°C, acetoacetanilide (15) forms and can be cyclized with concentrated sulfuric acid to 2-hydroxy-4-methylquinoline [607-66-9] (49). This example of kinetic vs thermodynamic control has been employed in the synthesis of many quinoline derivatives. They are useful as intermediates for the synthesis of chemotherapeutic agents (see Chemotherapeuticsanticancer). 

Another positive-working release by cyclization, illustrated by equation 5, starts with an immobile hydroquinone dye releaser (8), where R = alkyl and X is an immobilizing group. Cyclization and dye release take place in alkaU in areas where silver haUde is not undergoing development. In areas where silver haUde is being developed, the oxidized form of the mobile developing agent oxidizes the hydroquinone to its quinone (9), which does not release the... 

No oxidizing agent is required for the sulfuric acid promoted cyclization of iV,iV-diphenyl-hydroxylamine to carbazole (13CB3304). The parallel conversion of diphenyl sulfoxide and diphenyl selenoxide to dibenzothiophene (23CB2275) and dibenzoselenophene (39CR(199)53l) is effected by treatment with sodamide. 

The cyclization product is thermally unstable relative to Z-stilbene and reverts to starting material unless trapped by an oxidizing agent. The extent of eyclization is solvent-dependent, with nonpolar solvents favoring cyclization more than polar ones. ° Whereas the quantum yield for Z-E isomerization is nearly constant at about 35%, the cyclization... 

The first polyphosphino maeroeyeles designed speeifieally for use as transition metal binders were reported in 1977 in back-to-baek eommunications by Rosen and Kyba and their eoworkers. The maeroeyeles reported in these papers were quite similar in some respeets, but the synthetic approaches were markedly different. DelDonno and Rosen began with bis-phosphinate 18. Treatment of the latter with Vitride reducing agent and phosphinate 19, led to the tris-phosphine,20. Formation of the nickel (II) complex of 20 followed by double alkylation (cyclization) and then removal of Ni by treatment of the complex with cyanide, led to 21 as illustrated in Eq. (6.15). The overall yield for this sequence is about 10%. 

The first example of a cyclization of fluorine-containing 5-hexenyl radicals was the study of the radical-iniOated cyclodimenzation reaction of 3,3,4,4-tetra-fluoro-4-iodo-1-butene. In this reaction, the intermediate free radical adds either to more of the butene or to an added unsaturated species [54, 55] (equation 56). Electron-deficient alkenes are not as effective trapping agents as electron-nch alkenes and alkynes [55]. 

The Bischler-Napieralski reaction involves the cyclization of phenethyl amides 1 in the presence of dehydrating agents such as P2O5 or POCI3 to afford 3,4-dihydroisoquinoline products 2. This reaction is one of the most commonly employed and versatile methods for the synthesis of the isoquinoline ring system, which is found in a large number of alkaloid natural products. The Bischler-Napieralski reaction is also frequently used for the conversion of N-acyl tryptamine derivatives 3 into p-carbolines 4 (eq 2). 

A -cyclopropylquinolone 63 and iV-fused pyrrolidinyl 66 and piperidinyl 69 quinolones were reported as intermediates for the preparation of potent antibacterial agents. Use of acids as reaction solvent allow for the cyclization of these iV-substituted... 

Final structure determination of the monomethyl derivatives was made possible only on performing straightforward syntheses of the compounds, analogous to syntheses of allantoxaidine. The 1-methyl (19) and 3-methyl (20) derivatives were prepared by cyclization of 1- and 3-methyl biuret,respectively. The 3-methyl derivative was also obtained by cyclization of A ,A -bis(methylcarbamyl)formami-dxne. The 1-methyl derivative was the same as the product obtained by Biltz on methylation of silver salt of allantoxaidine with methyl iodide. The same product is formed primarily during methylation of dioxotriazine with diazomethane. An excess of this agent produces the expected 1,3-dimethyl derivative (21). These results of alkyl-... 

Diaminopyrimidines fused to a number of heterocycles (35) were also cyclized with one-carbon inserting agents to the corresponding hetero-cyclo-l,2,4-triazolo[l,5-c]pyrimidines 36 (75M1111 81JHC43 97JIC27). 

Diethyl oxalate functioned as one-carbon rather than two-carbon cyclizing agent with the diamino-heterocyclopyrimidines 37 to give the triazo-lopyrimidines 38. Diethyl malonate, ethyl acetoacetate, or ethyl... 

Cyclization of 1,2,4-Triazoles Having a -C-C-N Appendage at C3 with One-Carbon Cyclizing Agents... 

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