A Novel Efficient Synthesis of 1-Ethoxyvinyl Esters and Their Use in Acylation of Amines and Alcohols: Synthesis of Water-Soluble Oxaunomycin Derivatives

Kita, Yasuyuki; Maéda, Hiroshi; Omori, Kana; Okuno, Takayuki; Tamura, Yasumitsu

doi:10.1055/s-1993-22428

Cited by 69 publications

(37 citation statements)

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“…It has been observed that the regioselectivity of enol‐ester formation is determined by the coordination mode of the alkyne to the metal center . In the case of η 2 ‐binding, the nucleophile prefers the more substituted center β‐carbon (C β ), and hence the Markovnikov product is preferred . On the other hand, if the η 2 ‐alkyne tautomerizes to the η 1 ‐vinylidene form, then the nucleophilic attack at α‐carbon (C α ) will lead to the anti‐Markovnikov product .…”

Section: Introductionmentioning

confidence: 99%

Solvent‐Promoted Regio‐ and Stereoselectivity in Ru‐Catalyzed Hydrocarboxylation of Terminal Alkynes: A DFT Study

Maity

Koley

2017

ChemCatChem

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DFT calculations at the M06L‐D3(SMD)/LANL2TZ(f)/6‐311+G(d,p)//M06L/LANL2DZ/6‐31G(d)* level were performed to explore the mechanism, solvent effect, and origin of selectivity in the hydrocarboxylation of terminal alkynes catalyzed by (PCy3)2(CO)RuHCl. This catalytic system offers a unique example in which selectivity in enol‐ester synthesis is controlled in presence of different solvent media under mild reaction conditions. In CH2Cl2 solvent the regioselective gem‐enol‐ester (Pg) was preferred, whereas stereoselective Z‐enol‐ester (PZ) was observed exclusively in THF medium. We have unraveled the complete catalytic mechanism involving the following steps: a) alkyne coordination with subsequent nucleophilic attack and, finally, b) product elimination leading to the Markovnikov product Pg in both solvent media. Herein, the rate‐limiting nucleophilic attack step requires an activation barrier of 20.5 (21.0) kcal mol−1, which is 5.7 (5.6) kcal mol−1 lower than the crucial vinylidene formation step encountered for anti‐Markovnikov addition. Interestingly, a new reaction avenue unfolds under explicit THF medium, in which the inherent coordinating nature of the solvent becomes effective in altering the product regioselectivity. Under such an event, a highly facile ligandassisted proton shuttle (LAPS) mechanism is propagated, leading to vinylidene complex 11A. This intriguing mechanistic scenario facilitates favorably furnishing the PZ product rather than the Pg isomer by 4.3 kcal mol−1.

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Section: Introductionmentioning

confidence: 99%

Solvent‐Promoted Regio‐ and Stereoselectivity in Ru‐Catalyzed Hydrocarboxylation of Terminal Alkynes: A DFT Study

Maity

Koley

2017

ChemCatChem

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“…To explain the regioselectivity of the nucleophilic attack at the C-2 position of the alkyne,t he species B and C have been postulated as reactivei ntermediates. [4,16,26] Ther esulting enol ester D undergoesa ni ntramolecular transesterification to the alkenyl derivative E,which after keto-enol tautomerizationand protonation releases the b-oxo ester andr egenerates the catalytically active ruthenium species (Scheme 3). [27][28][29] Thef irst catalytic system which was able to generate b-oxo estersw as described by Mitsudo andW atanabe.…”

Section: Introductionmentioning

confidence: 99%

Atom Economic Ruthenium‐Catalyzed Synthesis of Bulky β‐Oxo Esters

et al. 2015

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Ruthenium complexes with the formulae Ru(CO) 2 (PR 3 ) 2 (O 2 CPh) 2 [6a-h;R = n-Bu, p-MeO-C 6 H 4 , p-Me-C 6 H 4 ,P h, p-Cl-C 6 H 4 , m-Cl-C 6 H 4 , p-CF 3 -C 6 H 4 , m,m'-(CF 3 ) 2 C 6 H 3 ]w ere prepared by treatment of triruthenium dodecacarbonyl [Ru 3 (CO) 12 ]w ith the respective phosphine and benzoic acid or by the conversion of Ru(CO) 3 (PR 3 ) 2 (8e-h)w ith benzoic acid. During the preparation of 8,r uthenium hydride complexes of type Ru(CO)(PR 3 ) 3 (H) 2 (9g, h)c ould be isolated as side products. Them olecular structures of the newly synthesizedc omplexes in the solid state are discussed. Compounds 6a-h were found to be highly effective catalysts in the addition of carboxylic acids to propargylic alcohols to give valuable b-oxo esters.T he catalyst screening revealed ac onsiderably influence of the phosphine'se lectronicn ature on the resulting activities. Theb est performances were obtained with complexes 6g and 6h,f eaturing electron-withdrawing phosphine ligands.A dditionally,c atalyst 6g is very active in the conversion of sterically demanding substrates,l eading to ab road substrate scope.T he catalytic preparation of simple as wella sc hallenging substrates succeeds with catalyst 6g in yields that often exceed those of established literature systems.F urthermore,t he reactions can be carriedo ut with catalyst loadings down to 0.1 mol% andr eactiont emperatures down to 50 8 8C.

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“…Installation of the O-acyl ketene acetal is deferred until the late stages of the synthesis, at which point conformational biases of the rigid framework are expected to stabilize this otherwise labile structural element. 12 Nelson and Stoltz recently reported progress toward the synthesis of the basiliolides and transtaganolides, 13 including an encouraging IMPDA reaction of a 3-bromo-2-pyrone. However, their system lacks an appropriate handle at the 5-position of the pyrone for further elaboration, and the bromine atom inserted late in the sequence to activate the key IMPDA reaction had to be removed in a subsequent step.…”

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confidence: 99%