- Origins of Regioselectivity in Iridium Catalyzed Allylic Substitution
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Detailed studies on the origin of the regioselectivity for formation of branched products over linear products have been conducted with complexes containing the achiral triphenylphosphite ligand. The combination of iridium and P(OPh)3 was the first catalytic system shown to give high regioselectivity for the branched product with iridium and among the most selective for forming branched products among any combination of metal and ligand. We have shown the active catalyst to be generated from [Ir(COD)Cl]2 and P(OPh)3 by cyclometalation of the phenyl group on the ligand and have shown such species to be the resting state of the catalyst. A series of allyliridium complexes ligated by the resulting P,C ligand have been generated and shown to be competent intermediates in the catalytic system. We have assessed the potential impact of charge, metal-iridium bond length, and stability of terminal vs internal alkenes generated by attack at the branched and terminal positions of the allyl ligand, respectively. These factors do not distinguish the regioselectivity for attack on allyliridium complexes from that for attack on allylpalladium complexes. Instead, detailed computational studies suggest that a series of weak, attractive, noncovalent interactions, including interactions of H-bond acceptors with a vinyl C - H bond of the alkene ligand, favor formation of the branched product with the iridium catalyst. This conclusion underscores the importance of considering attractive interactions, as well as repulsive steric interactions, when seeking to rationalize selectivities.
- Madrahimov, Sherzod T.,Li, Qian,Sharma, Ankit,Hartwig, John F.
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p. 14968 - 14981
(2015/12/08)
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- Ruthenium-catalysed linear-selective allylic alkylation of allyl acetates
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The regioselectivity in the ruthenium-catalysed allylic alkylation of mono substituted allyl acetates with the malonate anion was highly controlled by Ru3(CO)12 with 2-(diphenylphosphino)benzoic acid, and the linear-type alkylated product was obtained. The Royal Society of Chemistry.
- Kawatsura, Motoi,Ata, Fumio,Wada, Shohei,Hayase, Shuichi,Uno, Hidemitsu,Itoh, Toshiyuki
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p. 298 - 300
(2007/10/03)
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- Retention of regiochemistry of monosubstituted allyl acetates in the ruthenium catalysed allylic alkylation with malonate anion
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In the RuCl2(p-cymene)/PPh3 catalysed regioselective allylic alkylation of monosubstituted allyl acetates with malonate anion, the selective substitution at the position originally substituted with acetate was observed. The Royal Society of Chemistry.
- Kawatsura, Motoi,Ata, Fumio,Hayase, Shuichi,Itoh, Toshiyuki
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p. 4283 - 4285
(2008/03/28)
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- Molybdenum(0) and tungsten(0) catalysts with enhanced reactivity for allylic substitution: Regioselectivity and solvent effects
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The binuclear Mo(II) and W(II) complexes 28a,b and 29a,b have been developed as pre-catalysts for allylic substitution with β-dicarbonyl nucleophiles. These complexes are reduced in situ to Mo(0) and W(0) catalytic species 30a,b and 31a,b by excess of NaH, employed to generate sodiomalonate nucleophiles, or by DIBAL-H. 1,3-Dioxolane and 1,4-dioxane, when used as solvents, substantially accelerate the reaction. These new catalysts exhibit "traditional" Mo regiochemistry, i.e., the nucleophilic attack occurring preferentially at the more substituted carbon (5 → 9; 37 → 38), unless an additional factor, such as further coordination to another moiety of the allylic electrophile takes part (41), as in the case of the geranyl-type substrates (32 or 33 → 36).
- Malkov,Baxendale,Mansfield,Kocovsky
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p. 1234 - 1240
(2007/10/03)
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- Retention of regiochemistry of allylic esters in palladium-catalyzed allylic alkylation in the presence of a MOP ligand
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In the palladium-catalyzed allylic alkylation of (E)-3-substituted-2-propenyl acetates (1), 1-substituted-2-propenyl acetates (2), and 1- or 3-deuterio-2-cyclohexenyl acetate (5), which proceeds through 1,3-unsymmetrically substituted π-allylpalladium intermediates, selective substitution at the position originally substituted with acetate was observed by use of a sterically bulky monodentate phosphine ligand, 2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl (MeO-MOP). Studies of the structure of π-allylpalladium complexes generated by mixing [PdCl(π-cyclohexenyl)]2 with 1 or 2 equiv of MeO-MOP (L*) revealed that cationic bisphosphine complex [Pd(L*)2(π-cyclohexenyl)]+Cl- is not formed even in the presence of excess ligand but neutral monophosphine complex PdCl(L*)(π-cyclohexenyl) (11) is formed, leaving excess ligand free, and that the exchange of the coordination site of Cl and L* in 11 is much slower than that in triphenylphosphine complex PdCl(PPh3)(π-cyclohexenyl) (13). The slow exchange can rationalize the retention of regiochemistry in the allylic alkylation catalyzed by palladium/MeO-MOP complex.
- Hayashi, Tamio
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p. 1681 - 1687
(2007/10/03)
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- Derivatives of 2-amino-2′-diphenylphosphino-1,1′-binaphthyl (MAP) and their application in asymmetric palladium(O) -catalyzed allylic substitution
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CR)-(+)-2-Amino-2′-hydroxy-1,1′-binaphthyl (NOBIN, 5) can be readily converted into a series of novel N,N-disubstituted aminophosphines 9 and 23-25. The N,N-dimethyl derivative (R)-9 (MAP) was prepared via a sequence involving reductive alkylation with CH2O and NaBH4 (5 → 6), Pd-(0)-catalyzed coupling of the corresponding triflate with Ph2P(O)H (7 → 8), and reduction of the resulting phosphine oxide with Cl3SiH (8 → 9). Variation of this scheme was required for the preparation of 23-25 as the phosphinylation failed in the presence of bulky N substituents; the N-protected triflate 17 was first coupled with Ph2P(O)H, and the resulting phosphine oxide 18 was reduced with ClaSiH to give the aminophosphine 19, which was then subjected to reductive alkylation with individual ketones and NaBH4. The new P,N-binaphthyls thus obtained (23-25 and 9) were utilized as chiral ligands in Pd(0)-catalyzed allylic substitution. The enantioselectivites obtained for racemic 1,3-diphenylprop-2-en-l-yl acetate (±)-26 and malonate nucleophiles, which gave (S)-(-)-28, (-)-(+)-29, and (A)-(+)-30 as the respective products (in up to 71-73% ee at room temperature with Cs2CO3 in C2Cl2s and 9 or 23 as a ligand), are interpreted in terms of the chelated transition state 37 and preferential attack at the allylic terminus that is trans with respect to the phosphorus acceptor atom.
- Vyskocil, Stepan,Smrcina, Martin,Hanus, Vladimir,Polasek, Miroslav,Kocovsky, Pavel
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p. 7738 - 7748
(2007/10/03)
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- Regiocontrol in palladium-catalysed allylic alkylation by addition of lithium iodide
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Regioselectivity in the palladium-catalysed allylic alkylation of 1-arylprop-2-enyl acetates [ArCH(OAc)CH=CH2] or (E)-3-phenylprop-2-enyI acetate (PhCH=CHCH2OAc) with sodium enolates of soft carbon nucleophiles is controlled by addition of a catalytic amount of lithium iodide to give lienar products [(E)-ArCH=CHCH2Nu] exclusively; their branch isomers [ArCH(Nu)CH=CH2] were not detected.
- Kawatsura, Motoi,Uozumi, Yasuhiro,Hayashi, Tamio
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p. 217 - 218
(2007/10/03)
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- Regio- and enantio-selective allylic alkylation catalysed by a chiral monophosphine-palladium complex
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Allylic alkylation of racemic 1-arylprop-2-enyl acetates [ArCH(OAc)CH=CH2] with the sodium enolate of dimethyl methylmalonate in the presence of a palladium catalyst coordinated with (R)-2-diphenylphosphino-2′-methoxy-1,1′-binaphthyl [(R)-MeO-MOP] proceeds with high branch selectivity (90%) to give chiral products [ArC*H-(Nu)CH=CH2] of up to 87% ee.
- Hayashi, Tamio,Kawatsura, Motoi,Uozumi, Yasuhiro
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p. 561 - 562
(2007/10/03)
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