- Catalytic Activation of Unstrained C(Aryl)-C(Alkyl) Bonds in 2,2′-Methylenediphenols
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Catalytic activation of unstrained and nonpolar C-C bonds remains a largely unmet challenge. Here, we describe our detailed efforts in developing a rhodium-catalyzed hydrogenolysis of unstrained C(aryl)-C(alkyl) bonds in 2,2′-methylenediphenols aided by removable directing groups. Good yields of the monophenol products are obtained with tolerating a wide range of functional groups. In addition, the reaction is scalable, and the catalyst loading can be reduced to as low as 0.5 mol %. Moreover, this method proves to be effective to cleave C(aryl)-C(alkyl) linkages in both models of phenolic resins and commercial novolacs resins. Finally, detailed experimental and computational mechanistic studies show that with C-H activation being a competitive but reversible off-cycle reaction, this transformation goes through a directed C(aryl)-C(alkyl) oxidative addition pathway.
- Dong, Guangbin,Ratchford, Benjamin L.,Xue, Yibin,Zhang, Rui,Zhu, Jun
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p. 3242 - 3249
(2022/02/23)
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- Aromatic substitution in ball mills: Formation of aryl chlorides and bromides using potassium peroxomonosulfate and NaX
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Aryl chlorides and bromides are formed from arenes in a ball mill using KHSO5 and NaX (X = Cl, Br) as oxidant and halogen source, respectively. Investigation of the reaction parameters identified operating frequency, milling time, and the number of milling balls as the main influencing variables, as these determine the amount of energy provided to the reaction system. Assessment of liquid-assisted grinding conditions revealed, that the addition of solvents has no advantageous effect in this special case. Preferably activated arenes are halogenated, whereby bromination afforded higher product yields than chlorination. Most often reactions are regio- and chemoselective, since p-substitution was preferred and concurring side-chain oxidation of alkylated arenes by KHSO5 was not observed. The Royal Society of Chemistry.
- Schmidt, Robert,Stolle, Achim,Ondruschka, Bernd
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p. 1673 - 1679
(2013/02/22)
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- CHIRAL PHOSPHORUS COMPOUNDS
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The present invention provides P-chiral compounds of general formula (II) and (III): wherein at least one of R21, R25, R26 and R30 is independently selected from C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; at least one of R22, R24, R27 and R29 are independently selected from C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy and the remaining substituents selected from R22, R24, R27 and R29 are hydrogen; and R23 and R28 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy; Formula (III): wherein at least one of R21, R25, R26 and R30 is independently selected from phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; and R22, R23, R24, R27, R28 and R29 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy.wherein at least one of R21, R25, R26 and R30 is independently selected from phenyl and benzyloxy and the remaining substituents selected from R21, R25, R26 and R30 are hydrogen; and R22, R23, R24, R27, R28 and R29 are independently selected from hydrogen, C1-4 alkyl, CF3, C1-4 alkoxy, phenyl and benzyloxy.
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Page/Page column 31
(2008/12/04)
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- Synthesis and antioxidant profile of all-rac-α-selenotocopherol
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all-rac-α-Selenotocopherol (6c) has been synthesized in 11 steps in 6.6% total yield. Key steps include chloromethylation to approach the persubstituted aromatic 9b and cyclization of alcohol precursor 10 by radical homolytic substitution at selenium to f
- Shanks, David,Amorati, Riccardo,Fumo, Maria Grazia,Pedulli, Gian Franco,Valgimigli, Luca,Engman, Lars
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p. 1033 - 1038
(2007/10/03)
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- Novel Antioxidants: Unexpected Rearrangements in the Radical Cyclization Approach to 2,3-Dihydrobenzo[b]thiophene-5-ol Derivatives
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The novel α-tocopherol analogue 3,3,4,6,7-pentamethyl-2,3-dihydrobenzo[b]thiophene-5-ol (4a) was prepared by cyclodehydration of the aryl 2-hydroxyalkyl sulfide 6 in concentrated sulfuric acid. Aromatic bromination and dehydration of alcohol 6 furnished the 2-bromoaryl methallyl sulfide 10a as the kinetic product and the 2-bromoaryl 2-methyl-2-propenyl sulfide 11a as the thermodynamic one. Radical cyclization of these compounds afforded the desired 2,3-dihydrobenzo[b]-thiophene derivative 12 in addition to a rearranged isomer 13 thereof. It is proposed that the transformation of compound 10a to 13 occurs via 6-endo cyclization, β-scission, and subsequent 5-exo cyclization. The radical cyclization of the 2-bromoaryl allyl sulfide 16, unsubstituted in the allylic moiety, furnished only 2,3-dihydrobenzo[b]thiophene-5-ol derivative 17.
- Malmstroem, Jonas,Gupta, Vijay,Engman, Lars
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p. 3318 - 3323
(2007/10/03)
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- Structure-activity relationships for inhibition of inosine monophosphate dehydrogenase by nuclear variants of mycophenolic acid
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Structure-activity relationships in the region of the phthalide ring of the inosine monophosphate dehydrogenase inhibitor mycophenolic acid have been explored. Replacement of the lactone ring with other cyclic moieties resulted in loss of potency, especia
- Nelson, Peter H.,Carr, Stephen F.,Devens, Bruce H.,Eugui, Elsie M.,Franco, Fidencio,Gonzalez, Carlos,Hawley, Ronald C.,Loughhead, David G.,Milan, David J.,Papp, Eva,Patterson, John W.,Rouhafza, Sussan,Sjogren, Eric B.,Smith, David B.,Stephenson, Rebecca A.,Talamas, Francisco X.,Waltos, Ann-Marie,Weikert, Robert J.,Wu, John C.
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p. 4181 - 4196
(2007/10/03)
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- SELECTIVE MONOBROMINATION OF PHENOLS
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A method is proposed for the selective monobromination of the hydroxy derivatives of benzene with bis(dimethylacetamide)hydrogen tribromide in aprotic media as brominating agent.
- Mikhailov, V. A.,Savelova, V. A.,Rodygin, M. Yu.
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p. 1868 - 1870
(2007/10/02)
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- Process for producing trimethyl-p-benzoquinone
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A process for producing trimethyl-p-benzoquinone by halogenating 2,3,5- or 2,3,6-trimethylphenol and oxidizing the resulting 2,3,5- or 2,3,6-trimethyl-4-halogenophenol, is disclosed. The resulting compound can readily be converted to trimethylhydroquinone useful as a starting material for producing vitamin E.
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