73569-69-4Relevant articles and documents
Mechanism-Based Approach to Reagent Selection for Oxidative Carbon?Hydrogen Bond Cleavage Reactions
Floreancig, Paul E.,Liu, Peng,Miller, Jenna L.,Zhou, Lin
supporting information, (2021/12/09)
Numerous hydride-abstracting agents generate the same cationic intermediate, but substrate features such as intermediate cation stability, oxidation potential, and steric environment can influence reaction rates in an oxidant-dependent manner. This manusc
Ion pairing effects on the regioselectivity of arylic versus benzylic C-O bond reductive cleavage: synthetic applications
Azzena, Ugo,Dettori, Giovanna,Mascia, Ilaria,Pisano, Luisa,Pittalis, Mario
, p. 11998 - 12006 (2008/03/14)
The regioselectivity of the reductive cleavage of 3,4,5-trimethoxybenzyl methyl ether strongly depends on the alkali metal employed as a reducing agent and solvent effects. Reactions run using Na as a reducing agent led to aromatic C(4)-O bond cleavage, whilst reductions run in the presence of Na/15-crown-5, or using Li as a reducing agent, led to highly regioselective benzylic C-O bond cleavage. This regioselectivity turnaround is discussed in terms of major solvent effects affecting the fragmentation paths of a common reaction intermediate. Synthetic applications of these findings led to the synthesis of biologically active compounds, like 2,5-dialkyl-substituted resorcinols, or 1-(3,4,5-trimethoxyphenyl)-2-arylethanes structurally related to combretastatin.
Synthetic study for two 2H-chromenic acids, 8-chlorocannabiorcichromenic acid and mycochromenic acid
Yamaguchi, Seiji,Nedachi, Masahiro,Maekawa, Mikiko,Murayama, Yohei,Miyazawa, Masahiro,Hirai, Yoshiro
, p. 29 - 41 (2007/10/03)
Two 2H-chromenes having a fully substituted benzene ring, 8-chlorocannabioreichromene (1) and mycochromenic acid (2), were synthesized by a condensation of salicylaldehydes with isopropylidenemalonate or the thermal cyclization of corresponding propargyl ethers.
1,3-Dimethoxy-5-methylene-1,3-cyclohexadiene Compounds with Leaving Groups at C6: Generation, Solvolytic Reactivity, and Their Importance in the Photochemistry of 3,5-Dimethoxybenzyl Derivatives
DeCosta,Howell,Pincock,Pincock,Rifai
, p. 4698 - 4705 (2007/10/03)
The photochemistry of 3,5-dimethoxybenzyl compounds with the leaving groups acetate (1a), chloride (1b), bromide (1c), iodide (1d), diethyl phosphate (1e), and trimethylamine (1f), as the chloride, was examined by both product studies and flash photolysis. The isomeric triene, 5-methylene-1,3-cyclohexadiene derivative was observed for the acetate (2a), diethyl phosphate (2e) and trimethylammonium chloride (2f). The solvolysis of these derivatives, 2, was examined in alcohol solvents and the rate correlation with YOTS values gave m = 0.47 (2a) and 0.63 (2e), suggesting SN1 reactivity but with an early transition state. Quantum yields for formation of 2a and 2e indicated that these trienes play only a minor role (～16%) in the overall photochemistry of the corresponding arylmethyl substrates.
The Photochemistry of Methoxy-Substituted Benzyl Acetates and Benzyl Pivalates: Homolytic vs Heterolytic Cleavage
Pincock, J. A.,Wedge, P. J.
, p. 5587 - 5595 (2007/10/02)
The multiple methoxy-substituted benzyl acetates (3g-i) and benzyl pivalates (4g-i) have been photolyzed in methanol solution.The products of these reactions are derived from two critical intermediates; the benzyl radical/acyloxy radical pair and the benzyl cation/carboxylate anion pair.As predicted by the meta effect, the yield of ion-derived product, the methyl ether in this case, was enhanced by the presence of the m-methoxy groups.The yield of ether, for the acetate esters, varied from 2percent for the 4-methoxy-substituted ester to 66percent for the 3,4,5-trimethoxy-substituted ester.In contrast, the yield of ether, for the pivalate esters, varied from 1percent for the 4-methoxy-substituted ester to 20percent for the 3,4,5-trimethoxy-substituted one.The meta effect does not explain these differences; electron transfer converting the radical pair to the ion pair is still an important pathway in the mechanism for ion formation.A quantitative analysis of the yield of the ethers was done in order to obtain the electron-transfer rate constants.This analysis revealed that the yield of the ethers was higher than expected based on previous results for other substituted benzyl acetates.A possible explanation for this discrepancy is that internal return of the radical pair to starting material for the acetate esters is more efficient than for the pivalate esters.Also, the esters 3k and 3l, were prepared to study the effect of electron-withdrawing groups in the meta position.For these esters, the benzylic cleavage reactions were inefficient and an isomerization reaction, the benzvalene rearrangement, was competitive.
Deoxygenation of Highly Hindered Phenols
Saa, Jose M.,Dopico, Mercedes,Martorell, Gabriel,Garcia-Raso, Angel
, p. 991 - 995 (2007/10/02)
Highly hindered phenolic compounds can be efficiently deoxygenated by reduction of the corresponding triflates under homogeneous or heterogeneous (Pd/C) conditions.Reductive deoxygenation under homogeneous conditions has been shown to occur both in the presence of acid (HCOOH, CH3COOH, (CH3)3CCOOH, PhCH2COOH) or in its absence.The concomitant formation of dibutylformamide apparently derives from aminolysis of DMF by dibutylamine, the Pd(0)-catalyzed hydrolysis product of tributylamine.Deuteration experiments suggest that several hydrogen (or deuterium) sources operate in the hydrogenolysis processes studied.
Synthetic Confirmation of the Structure of the Lichen Benzyl Esters Alectorialic and Barbatolic Acids
Elix, John A.,Jayanthi, Vilas K.
, p. 1841 - 1850 (2007/10/02)
The total synthesis of methyl alectorialate (3) and methyl barbatolate (4) has been achieved, and the synthetic esters have been compared with naturally derived material.In addition alectorialin (decarboxylalectorialic acid) (5) and barbatolin (6) have be
SUBSTITUENT EFFECTS IN THE PHOTOSOLVOLYSIS OF BENZYL DERIVATIVES. GENERAL STRUCTURE-REACTIVITY RELATIONSHIPS.
Wan, Peter,Chak, Becky,Li, Carrier
, p. 2937 - 2940 (2007/10/02)
The relative reactivity of photosolvolysis of a number of substituted benzyl acetates is in the order ortho > meta > para, these substitutent effects being apparently additive, as suggested by the relative reactivity of photomethanolysis of several dimethoxy-susbstituted benzyl alcohols.
Structure-Reactivity Studies and Catalytic Effects in the Photosolvolysis of Methoxy-substituted Benzyl Alcohols
Wan, Peter,Chak, Becky
, p. 1751 - 1756 (2007/10/02)
The photosolvolysis of several methoxy-, dimethoxy-, and hydroxy-substituted benzyl alcohols has been studied in aqueous solution.The primary photochemical event is photodehydroxylation, to give a benzyl cation intermediate, which can be trapped by added external nucleophiles.The reaction is via the singlet excited state, based on observation of fluorescence quenching by hydronium ion in a complementary manner with acid catalysis of reaction observed for several derivatives.Solvent isotope effects on fluorescence efficiency and reaction for (7) and (8) provide additional support of singlet-state reactivity for these compounds.Dimethoxy-substituted alcohols are more reactive than monosubstituted compounds, with quantum yields of methanolysis of up to 0.31 for the most reactive compound, 2,6-dimethoxybenzyl alcohol (8).Using a kinetic argument, the quantum yields of the primary photodehydroxylation process has been estimated to be 1.0 +/- 0.1 for this compound.The results observed for the dimethoxy-substituted derivatives suggest the existence of additivity of substituent effects in these photodehydroxylation reactions.
