178,972 research outputs found
Absolute rate constants for addition of aryl radicals to 1,4-benzoquinone and butane-2,3-dione. A new method for homolytic alkylation of quinones
No full textRate consts. were detd. for the addn. of 4-RC6H4• (R = H, MeO, Me, Cl, O2N) to 1,4-benzoquinone (I) and MeCOCOMe in DMSO. The aryl radicals show only a low sensitivity to polar effects. Arenediazonium salt-alkyl iodide mixts. were used to alkylate 1,4-naphthoquinone and I in DMSO. The method is versatile but gave only moderate yields (25-50% for monoalkylation and 5-15% for dialkylation), owing to the high reactivity of aryl radicals towards quinone
Stoichiometric and catalytic reactions of free radicals generated by metallic redox couples. Application to the synthesis of naphthalene derivatives
No full textA review with 13 refs. Radical reactions induced by monoelectronic redox metals proved useful in the synthesis of naphthols and dihydro- or tetrahydro-naphthalenes. Examples of either intra- or consecutive inter-intramol. oxidative radical alkylations of arom. are reported. The reactivity of carbon centered β-dicarbonyl, alkyl and vinyl radicals, generated in the presence of metallic salts Mn(III), Fe(III), Ce(IV), and the influence of the redox couple on the selectivity to the products are examd. The potentiality of the method is evidenced by the possibility to carry out such reactions in an electrocatalytic way with high yiel
Use of homolytic redox processes in organic syntheses
No full textA review with 36 refs. Examples of title redox processes are the oxidative alkylation of aroms. and the reductive alkylation of olefins promoted by metal salt
Homolytic aromatic alkylation of 1- and 2-alkoxynaphthalenes by manganese(III) oxidation of methanes or ethanes 1,1-disubstituted with electron-withdrawing groups
No full textThermal decompn. of Mn(OAc)3 in AcOH in the presence of MeCH(CO2Et)2 or CH2RR1 (R = Ac, R1 = H, Ac, CO2Et; R = CO2Et, R1 = cyano, CO2Et) and alkoxynaphthalenes I (R2 = H, R3 = OMe, OEt) and II (R4 = H, R5 = OMe, OCMe3) gave arom. substitution products, e.g., I [R2 = CMe(CO2Et)2, CHRR1, CRR1OAc, R3 = OMe, OEt] and II [R4 = CH(CO2Et)2, C(OAc)(CO2Et)2, R5 = OMe, OCMe3]. These reactions can also be performed with Mn(III) acetylacetonate and acetoacetate complexe
Free-Radical Diazo Coupling. A New General Reaction of Diazonium Salts
No full textWe now describe new general synthesis of alkylaryldiazenes on the basis of the reactions of Scheme I:
R- + N=N+-Ar -> RN=N.+-Ar (1)
RN=N.+-Ar + M"+ -> RN=NAr + M(n+1)+ (2)
of alkyl radicals to arenediazonium cations (eq 1) and reduction of the intermediate azo radical cation adducts by metal salts (M"+, eq 2). Several sources of alkyl radicals R. were found suitable for this reaction
Reductive arylation of electron-deficient olefins: 4-(4-chlorophenyl)butan-2-one
No full textBenzenediazonium compds. 4-RC6H4N2+ (R = H, Br, Cl, OMe, MeCO) were treated with R1CR2:CHR3 (R1 = H, Me, CHMe2, CMe3, Ph; R2 = H, Me; R3 = COMe, CHO, cyano, CO2H, CO2Et) and TiCl3 to yield reductive arylation products I. Thus, CH2:CHCOMe was added to TiCl3 in DMF under N, 4-ClC6H4N2+ Cl- was introduced slowly, and the mixt. was stirred to give 4-ClC6H4CH2CH2COMe - Ripubblicato in: Organic Syntheses, Coll. Vol. 7 (1990), 10
Reactivity of malonyl radicals. Synthesis of substituted dihydronaphthalenes by manganese(III) oxidation of diethyl .alpha.-benzylmalonate in the presence of alkynes
No full textOxidn. of di-Et α-benzylmalonate (I) by Mn(III) acetate in acetic acid at 70° in the presence of alkynes RC≡CR1 (R = cyclohexyl, CO2Et, Me3Si, Ph, CH2OH, R1 = H; R = R1 = Ph, Et, CO2Et, Pr; R = CO2Me, R1 = Me) leads to dihydronaphthalene derivs. II in moderate to good yields. A homolytic mechanism, involving oxidn. of I to the corresponding malonyl radical, its addn. to a triple bond, and intramol. homolytic arom. substitution of the vinyl radical adducts, is suggested. Propargylic hydrogen abstraction and dimerization at the malonic position for less reactive alkynes are the main side reactions obsd. Relative and abs. rates of addn. of α-benzylmalonyl radicals to representative alkynes and alkenes, deduced from competitive expts., indicate a lower reactivity toward alkynes than toward the corresponding substituted alkenes. Both SOMO-LUMO and SOMO-HOMO interactions in the transition state lower the activation energy of these homolytic addns. with alkenes, but only the SOMO-HOMO interaction dominates with the examd. alkynes. 2-Naphthoic acid derivs. can be efficiently obtained by oxidative decarboxylation of II with NaI and ai
Synthesis of substituted tetrahydronaphthalenes by manganese(III), cerium(IV), and iron(III) oxidation of substituted diethyl .alpha.-benzylmalonates in the presence of olefins
No full textOxidn. of 12 RR1CHCH(CO2Et)2 [R = (un)substituted Ph, R1 = H, Me] by Mn(OAc)3 in AcOH2, Ce(NH4)2(NO)6 in MeOH, or Fe(CHO4)3 in MeCN in the presence of 19 R2R3C:CHR4 [R2 = H, alkyl, alkenyl, Ph, AcO, EtO2C, cyano, etc.; R3 = H, Me3CCH2, Me, EtO2C, EtO2CCH:CH; R4 = H, Me, EtO2C; R2R4 = (CH2)4, CH:CHCH2] was studied. The results are consistent with a common mechanism involving selective generation of malonyl radicals from high-valent metal malonyl complexes, their addn. to the olefin, and competition of the adduct radical between intramol. cyclization to produce highly functionalized tetrahydronaphthalenes I (XC6H4 = R) and oxidn. by metal salt to give mainly γ-lactones II. Several electron-withdrawing and -releasing substituents on the arom. ring and on the olefin can be successfully used in the synthesis of I without olefin telomerization. The influence of metal and olefin or arom. substituents on the homolytic addn. and intramol. arom. substitution is discusse
Side-chain oxidation of dialkyl arylmalonates by manganese(III) acetate
No full textSide-chain oxidn. of PhCH(CO2R) (R = alkyl) and its derivs. by Mn(OAc)3 in AcOH, C6H6, and hexane, alone or in the presence of O or halide and pseudohalide ions (N3-, thiocyanate, Br-, Cl-) gives PhCR1(CO2R) (R1 = OAc, N3, thiocyanato, Br, Cl). The products obtained depend on the structure of the starting malonate and the reaction condition
Improved preparation of aminomethylenemalonic acid derivatives by tin-promoted addition of diethyl malonates to nitriles
No full text(H2N)CR:C(CO2Et)2 (R = Ph, Me, Me2CH, cyclohexyl, hexyl, Me2C:CH) were prepd. in 50-98% yields by refluxing CH2(CO2Et)2 with RCN in the presence of SnCl4 in CH2Cl
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