32360-28-4Relevant academic research and scientific papers
2-Quinoxalinol diamine Cu(II) complex: Facilitating catalytic oxidation through dual mechanisms
Li, Yuancheng,Lee, Taebum,Weerasiri, Kushan,Wang, Tanyu,Buss, Emily E.,McKee, Michael L.,Gorden, Anne E. V.
, p. 13578 - 13583 (2014/11/08)
The Cu(II) complex 1, Cu(II)-6-N-3,5-di-tert-butylsalicylidene-6,7- quinoxalinol-diamine, has been developed to address problems with current methods of catalytic oxidation using tert-butyl hydroperoxide (TBHP). Complex 1 demonstrated an increased capability to utilize TBHP while limiting interference from free radical reactions and was demonstrated to be highly effective in the oxidations of a variety of olefins. the Partner Organisations 2014.
Ammonium-directed dihydroxylation of 3-aminocyclohex-1-enes: Development of a metal-free dihydroxylation protocol
Aciro, Caroline,Claridge, Timothy D. W.,Davies, Stephen G.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.
supporting information; experimental part, p. 3751 - 3761 (2009/02/04)
Treatment of 3-aminocyclohex-1-enes with mCPBA in the presence of trichloroacetic acid gives the corresponding 1,2-anti-2,3-syn-1- trichloroacetoxy-2-hydroxy-3-aminocyclohexane with high levels of diastereoselectivity (90% de). This is consistent with a mechanism of oxidation involving hydrogen-bonded delivery of the oxidant by the allylic ammonium ion formed in situ, followed by highly regioselective ring-opening of the intermediate epoxide by trichloroacetic acid. The effect of conformational constraints upon the oxidation reaction is also examined. The Royal Society of Chemistry 2008.
Chiral hydroperoxides as oxygen source in the catalytic stereoselective epoxidation of allylic alcohols by sandwich-type polyoxometalates: Control of enantioselectivity through a metal-coordinated template
Adam, Waldemar,Alsters, Paul L.,Neumann, Ronny,Saha-Moeller, Chantu R.,Seebach, Dieter,Beck, Albert K.,Zhang, Rui
, p. 8222 - 8231 (2007/10/03)
The epoxidation of allylic alcohols is shown to be efficiently and selectively catalyzed by the oxidatively resistant sandwich-type polyoxometalates, POMs, namely [WZnM2(ZnW9O 34)2]q- [M = OV(IV), Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], with organic hydroperoxides as oxygen source. Conspicuous is the fact that the nature of the transition metal M in the central ring of polyoxometalate affects significantly the reactivity, chemoselectivity, regioselectivity, and stereoselectivity of the allylic alcohol epoxidation. For the first time, it is demonstrated that the oxovanadium(IV)-substituted POM, namely [ZnW(VO)2(ZnW 9O34)2]12-, is a highly chemoselective, regioselective, and also stereoselective catalyst for the clean epoxidation of allylic alcohols. A high enantioselectivity (er values up to 95:5) has been achieved with [ZnW(VO)2(ZnW9O 34)2]12- and the sterically demanding TADOOL-derived hydroperoxide TADOOH as regenerative chiral oxygen source. Thus, a POM-catalyzed asymmetric epoxidation of excellent catalytic efficiency (up to 42 000 TON) has been made available for the development of sustainable oxidation processes. The high reactivity and selectivity of this unprecedented oxygen-transfer process are mechanistically rationalized in terms of a peroxy-type vanadium(V) template.
A highly chemoselective, diastereoselective, and regioselective epoxidation of chiral allylic alcohols with hydrogen peroxide, catalyzed by sandwich-type polyoxometalates: Enhancement of reactivity and control of selectivity by the hydroxy group through metal-alcoholate bonding
Adam, Waldemar,Alsters, Paul L.,Neumann, Ronny,Saha-Moeller, Chantu R.,Sloboda-Rozner, Dorit,Zhang, Rui
, p. 1721 - 1728 (2007/10/03)
Sandwich-type polyoxometalates (POMs), namely [VZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], are shown to catalyze selectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide under mild conditions (ca. 20 °C) in an aqueous/organic biphasic system. The transition metals M in the central ring of polyoxometalate do not affect the reactivity, chemoselectivity, or stereoselectivity of the allylic alcohol epoxidation by hydrogen peroxide. Similar selectivities, albeit in significantly lower product yields, are observed for the lacunary Keggin POM [PW11O39]7-, in which a peroxotungstate complex has been shown to be the active oxidizing species. All these features support a tungsten peroxo complex rather than a high-valent transition-metal oxo species operates as the key intermediate in the sandwich-type POM-catalyzed epoxidations. On capping of the hydroxy functionality through acetylation or methylation, no reactivity of these hydroxy-protected substrates [1a(Ac) and 1a(Me)] is observed by these POMs. A template is proposed to account for the marked enhancement of reactivity and selectivity, in which the allylic alcohol is ligated through metal - alcoholate bonding, and the H2O2 oxygen source is activated in the form of a peroxotungsten complex. 1,3-Allylic strain promotes a high preference for the threo diastereomer and 1,2-allylic strain a high preference for the erythro diastereomer, whereas tungsten - alcoholate bonding furnishes high regioselectivity for the epoxidation of the allylic double bond. The estimated dihedral angle α of 50 - 70° for the metal - alcoholate-bonded template of the POM/H2O2 system provides the best compromise between 1,2A and 1,3A strain during the oxygen transfer. In contrast to acyclic allylic alcohols 1, the M-POM-catalyzed oxidation of the cyclic allylic alcohols 4 by H2O2 gives significant amounts of enone.
Allylic CH oxidation versus epoxidation of 2-cyclohexenols, catalyzed by chromium- and manganese-substituted polyoxometalates and salen complexes
Adam, Waldemar,Herold, Marike,Hill, Craig L.,Saha-Moeller, Chantu R.
, p. 941 - 946 (2007/10/03)
2-Cyclohexenol (1) is oxidized chemoselectively to 2-cyclohexenone (2a) by the α-Keggin chromium-substituted polyoxometalate (POM) Ia as the catalyst and iodosobenzene as the oxygen source. For the chromium(salen) catalyst IIa the same chemoselectivity in favor of allylic CH oxidation is observed. The manganese-substituted POM Ib and the manganese(salen) complex IIb, however, afford appreciable amounts of the epoxy alcohol 2b. For the stereolabeled 5-tert-butyl-2-cyclohexenols 5, the diastereoselectivity of the epoxidation was appreciable (syn:anti 82:18) in the case of the manganese (salen) complex IIb with the cis isomer, while the manganese-substituted POM Ib exhibited no syn versus anti π-facial differentiation for the cis or trans diastereomer of the cyclohexenol 5. The observed syn hydroxy directivity for the manganese(salen) complex IIb is rationalized in terms of optimal hydrogen bonding between the MnV oxo complex IIb and the trans diastereomer of the allylic alcohol substrate 5. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany 2002.
Steric and electronic effects in the diastereoselective catalytic epoxidation of cyclic allylic alcohols with methyltrioxorhenium (MTO)
Adam, Waldemar,Mitchell, Catherine M.,Saha-Moeller, Chantu R.
, p. 785 - 790 (2007/10/03)
The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (E(s)) or Charton (v). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m- chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130°is suggested.
Mitsunobu Reaction of Unbiased Cyclic Allylic Alcohols
Shull, Brian K.,Sakai, Takashi,Nichols, Jeffrey B.,Koreeda, Masato
, p. 8294 - 8303 (2007/10/03)
The stereochemical inversion of unbiased allylic alcohols using triphenylphosphine, diethyl azodicarboxylate, and benzoic acid, commonly known as the Mitsunobu reaction, was studied in three different solvents with specific attention toward the product composition. The results generated for the Mitsunobu reaction of (R)-3-deuterio-2-cyclohexen-1-ol and the cis and trans isomers of 1-deuterio-5-methyl-2-cyclohexen-1-ol, 1-deuterio-5-tert-butyl-2-cyclohexen-1-ol, and optically active cis and trans 5-isopropyl-2-methyl-2-cyclohexen-1-ol all gave similar product distributions with respect to inversion and retention at the carbinol center as well-as syn and anti Sn2′ type addition when THF or benzene was used as the solvent (CH2Cl2 gave less selective product distributions). Interestingly, it was found that the quasi-equatorial and quasi-axial nature of the starting allylic alcohol does not appear to affect the product distribution for this reaction, nor does methyl substitution at the central carbon of the allylic alcohol. In all cases, significant amounts (8-28%) of non-SN2 type products were detected for these sterically unbiased allylic alcohols; only 72-77% of the product was from SN2 type reaction when sterically undemanding (R)-S-deuterio-2-cyclohexen-1-ol was subjected to Mitsunobu conditions.
On the dihydroxylation of cyclic allylic alcohols
Donohoe, Timothy J.,Garg, Rina,Moore, Peter R.
, p. 3407 - 3410 (2007/10/03)
The preparation and dihydroxylation (OsO4) of a series of conformationally constrained allylic alcohols is described. By using dichloromethane as solvent, the selectivity that favours the anti triol is substantially reduced by hydrogen-bonding
Solvent Effects in the Dimethyldioxirane Oxidation of Allylic Alcohols: Evidence for Hydrogen Bonding in the Dipolar Transition State of Oxygen Transfer
Adam, Waldemar,Smerz, Alexander K.
, p. 13039 - 13044 (2007/10/02)
A notably higher diastereoselectivity is observed in the dimethyldioxirane epoxidation of chiral allylic alcohols when less polar solvent mixtures are employed; this is interpreted in terms of a dipolar transition state with OH association through hydrogen bonding to the dioxirane, for which a preferential dihedral angle of >130 deg is estimated.
The enigmatic 1J(CH) coupling constants of allyl-type organometallic compounds
Schlosser, Manfred,Lehmann, Ruth,Jenny, Titus
, p. 149 - 157 (2007/10/02)
A new attempt has been made to identify the factors responsible for the abnormally small one-bond C, H coupling constants observed for allyl, pentadienyl and heptatrienylmetal compounds.In-plane deformations (widening of the central CCC angle) should have
