19928-57-5Relevant academic research and scientific papers
Palladium catalysed aryl enol ether synthesis from vinyl triflates
Willis, Michael C.,Taylor, Dawn,Gillmore, Adam T.
, p. 2222 - 2223 (2003)
Vinyl triflates can be efficiently converted into the corresponding aryl enol ethers by treatment with a phenol, NaOtBu and a catalyst generated from Pd2dba3 and 2-(di tBu-phosphino)biphenyl.
Merging α-Lithiation and Aldol-Tishchenko Reaction to Construct Polyols from Benzyl Ethers
Sedano, Carlos,Velasco, Rocío,Suárez-Pantiga, Samuel,Sanz, Roberto
, p. 8070 - 8075 (2020/11/02)
α-Lithiobenzyl ethers, generated by selective α-lithiation, undergo an aldol-Tishchenko reaction upon treatment with carboxylic esters and paraformaldehyde. The reaction of the organolithium with the carboxylate generates an intermediate enolate that, after formaldehyde addition, affords 1,2,3-triol derivatives in a straightforward and one-pot manner. These products are obtained as single diastereoisomers bearing a quaternary stereocenter. The complete diastereocontrol of the aldol-Tishchenko process is attributed to stereoelectronic preferences in the transition state.
Vinylation of Aryl Ether (Lignin Β-O-4 Linkage) and Epoxides with Calcium Carbide through C?O Bond Cleavage
Teong, Siew Ping,Lim, Jenny,Zhang, Yugen
, p. 3198 - 3201 (2017/09/02)
Calcium carbide has been increasingly used as a sustainable, easy-to-handle, and low-cost feedstock in organic synthesis. Currently, methodologies of using calcium carbide as “solid acetylene” in synthesis are strictly limited to activation and reaction w
Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes
Gómez-Suárez, Adrián,Oonishi, Yoshihiro,Martin, Anthony R.,Nolan, Steven P.
, p. 172 - 178 (2016/04/05)
Due to the synthetic advantages presented by the dual-gold-catalysed hydrophenoxylation of alkynes, a thorough study of this reaction was carried out in order to fully define the scope and limitations of the methodology. The protocol tolerates a wide range of functional groups, such as nitriles, ketones, esters, aldehydes, ketals, naphthyls, allyls or polyphenols, in a milder and more efficient manner than the previously reported methodologies. We have also identified that while we are able to use highly steric hindered phenols, small changes on the steric bulk of the alkynes have a dramatic effect on the reactivity. More importantly, we have observed that the use of substrates that facilitate the formation of diaurated species such as gem-diaurated or s,pdigold-acetylide species, hinder the catalytic activity. Moreover, we have identified that the use of directing groups in unsymmetrical alkynes can help to achieve high regioselectivity in the hydrophenoxylation.
Kinetics of breakdown of aryl hemiacetals of α-bromoacetophenone. Effect of phenol leaving groups on the lifetime of tetrahedral intermediates
MacClelland, Robert A.,Kanagasabapathy, V. M.,Mathivanan, N.
, p. 2084 - 2093 (2007/10/02)
The kinetics of breakdown of seven aryl hemiacetals of α-bromoacetophenone (TOH) have been examined, with aryl substituents 4-MeO, 4-Me, 3-Me, H, 3-MeO, 4-Cl, 3-Cl.The hemiacetals were generated as intermediates in the aqueous bromination of α-aryloxystyrenes, where the breakdown of the hemiacetal is the rate-limiting stage in the overall reaction.Base catalysis of the breakdown shows large Broenstedt β values (0.8-1.0) and similarly large βlg values (-0.8 to -1.0).These are argued to arise because of a preassociation mechanism in which the hydrogen-bonded intermediate TO-...HA loses aryloxide faster than diffusional separation of the acid-base pair.This mechanism is enforced by lifetimes of the deprotonated hemiacetals TO- in the 1010 - 1012 s-1 range.Such lifetimes were estimated in two independent ways, by extrapolation of data previously obtained for alkyl hemiacetals of α-bromoacetophenone, and through a calculation based upon the experimental catalytic coefficients, and estimates of the acidity constants for TOH and the equilibrium constants for formation of hydrogen-bonded complexes.The pH-independent breakdown has βlg = -1.03, and the point lies near the Broenstedt line for the carboxylate catalysis.This, therefore, also occurs by a preassociation mechanism with water as the catalyst forming the intermediate TP-...H3O+, which loses aryloxide faster than diffusional separation.Catalysis by hydroxide ion occurs with rate constants of 8*109 M-1 s-1 independent of aryl substituent.This represents rate-limiting diffusional encounter of the hemiacetal and hydroxide ion, the hydrogen-bonded intermediate TOH...OH-1 rapidly proceeding on to products.Acid catalysis of the hemiacetal breakdown occurs by a class "n" mechanism in which the acid assists departure of the substituted phenol.Alkyl hemiacetals of α-bromoacetophenone break down by a class "e" mechanism where the leaving group is fully protonated before bond cleavage.The class "e" mechanism can be excluded for the aryl derivatives, since rate constants much greater than diffusion are required to explain the observed catalytic coefficients.The different mechanism is followed in order to avoid the fully protonated hemiacetal, which, being of an O-protonated anisole structure, is of very high energy. Key words: hemiacetal kinetics, preassociation, intermediate lifetime
Alkylidenation of Ester Carbonyl Groups by means of a Reagent Derived from RCHBr2, Zn, TiCl4, and TMEDA. Stereoselective Preparation of (Z)-Alkenyl Ethers
Okazoe, Takashi,Takai, Kazuhiko,Oshima, Koichiro,Utimoto, Kiitiro
, p. 4410 - 4412 (2007/10/02)
Reagents prepared by reduction of 1,1-dibromoalkanes (R3CHBr2) with zinc and TiCl4 in the presence of N,N,N',N'-tetramethylethylenediamine in THF are effective in the conversion of esters (R1CO2R2) to the corresponding alkenyl ethers (R1(R2O)C=CHR3) with high Z selectivity.
Carbonyl Methylenation Using a Titanium- Aluminum (Tebbe) Complex
Pine, Stanley H.,Pettit, Robert J.,Geib, Gregory D.,Cruz, Susana G.,Gallego, Claudio H.,et al.
, p. 1212 - 1216 (2007/10/02)
The titanium-aluminum (Tebbe) complex is shown to be an effective methylenating agent for a variety of carbonyl groups.The reaction is unique in that the carbonyl groups of carboxylic acid derivatives are readily methylenated.Thus vinyl enol ethers are prepared from esters and enamines are formed from amides.The complex provides a method for methylenating hindered or base sensitive ketones that is advantageous to the Wittig reagent.Selective methylenation of dicarbonyl compounds is also accomplished.
β-PEROXYPROPIOLACTONES FROM CYCLOPROPANONE CYANOHYDRINS AND THEIR NOVEL REARRANGEMENT
Oku, Akira,Yokoyama, Taka-aki,Harada, Toshiro
, p. 4699 - 4702 (2007/10/02)
Air oxidation of cyclopropanone cyanohydrins produced β-peroxypropiolactones (2).The 3,3-diphenyl-substituted-2 was decomposed readily by the catalysis of silica gel to yield α-phenoxystyrene quantitatively.
