Hydroalkoxylation palladium

Recently, Y. Yamamoto reported a palladium-catalyzed hydroalkoxylation of methylene cyclopropanes (Scheme 6-25) [105]. Curiously, the catalysis proceeds under very specific conditions, i.e. only a 1 2 mixture of [Pd(PPh3)4] and P(o-tolyl)3 leads to an active system. Other combinations using Pd(0 or II) precursors with P(o-tolyl)3 or l,3-bis(diphenylphosphino)propane, the use of [Pd(PPh3)4] without P(o-tolyl)3 or with other phosphine ligands were all inefficient for the hydroalkoxylation. The authors assumed a mechanism in which oxidative addition of the alcohol to a Pd(0) center yields a hydrido(alkoxo) complex which is subsequently involved in hydropal-ladation of methylenecyclopropane. 

Hydration and Hydroalkoxylation of Alkynes Gold compounds were first applied to catalyze these types of reactions by Utimoto et al. in 1991, when they studied the use of Au(III) catalysts for the effective activation of alkynes. Previously, these reactions were only catalyzed by palladium or platinum(II) salts or mercury(II) salts under strongly acidic conditions. Utimoto et al. reported the use of Na[AuCI41 in aqueous methanol for the hydration of alkynes to ketones [13]. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

The transition metal-catalyzed addition of alcohols to unsaturated systems has not been widely investigated. Reports on addition of alcohols to 1,3-diene [24] or allene [25] have appeared but have very limited scope. We recently reported the palladium/benzoic acid-catalyzed inter- and intramolecular addition of alcohols to alkynes in which various acyclic and cyclic allylic ethers are produced [26], The Pd-catalyzed addition of alcohols to alkylidenecyclopropanes proceeds smoothly providing a powerful tool for synthesis of allylic ethers [27a]. An intramolecular version of the hydroalkoxylation has been demonstrated in which the phenol-tethered alkylidenecyclopropanes undergo facile cyclization to give exomethylene products [27b],... 

Both, hydration and hydroalkoxylation of olefins are usually carried out under acid catalysis or by oxymercuration reactions, although reactions mediated by palladium or by other metals have recently begun to emerge. In the latter case, nucleophilic addition of the O—H group is favored by a cationic palladium species that activates... 

The three component aminoallylation reaction of the activated olefins 4 was also reported by us (Scheme 7) [39]. The palladium catalyzed reaction between phthalimid 10, olefins 4 and allyl chloride 11 proceeded well in the presence of CS2CO3 to give the corresponding aminoallylation products 12 in high yields. Likewise, cyanoallylation of activated olefins was also reported (Scheme 8) [40]. In both cases only aryl substituded and f-bulyl substituded olefins are proved good substrates. The mechanism of these reactions is presumably similar to that of hydroalkoxylation reaction (see Scheme 5). 

Hydroalkoxylation of alkenols catalyzed by acids <05HCA3055 05OL4117>, silverfl) triflate <05OL4553>, palladium catalysts <05SL1609> and molybdenum catalysts <05CL790> has also been utilized in the formation of tetrahydrofurans. As can be seen... 

We reported that the intramolecular hydroamina-tion and hydroalkoxylation of the alkynes 285 in the presence of palladium/benzoic acid catalysts produced... 

Hydroalkoxylation of alkynes, or the addition of alcohol to alkynes, is a fundamental reaction in organic chemistry that allows the preparation of enol ethers and a variety of oxygen-containing heterocycles such as furan, pyran, and benzofuran derivatives. Bergbreiter et al. found that a Mnear poly-(A-isopropylacrylamide) (PNIPAM) polymer exhibited inverse temperature solubility in water (i.e., soluble in cold water but insoluble in hot water). A recoverable homogeneous palladium catalyst was prepared based on the polymer. The PNIPAM-bound Pd(0) catalyst was effective for the reaction of 2-iodophenol with phenylacetylene in aqueous THE media to give the target product... 

Internal alkynes were oxidatively fragmented into two molecules of carboxylic esters by a palladium catalyst under an oxygen atmosphere (Scheme 7.53) [72]. It is proposed that palladium initially induces hydroalkoxylation of diphenylacetylene to produce the enol ether 155. [2+2] Cycloaddition of 155 with molecular oxygen ensues to furnish the 1,2-dioxetane 156, which is then fragmented into methyl benzoate and benzaldehyde. Benzaldehyde is further oxidized to methyl benzoate under the oxidative reaction conditions. 

The hydroalkoxylation of an internal alkyne to afford a spiroacetal was first described by Utimoto in 1983 [85]. Using PdCl2 or PdCl2(PhCN)2 as catalyst, the spiroacetals 158 were obtained in high yield (Scheme 39). The method was not adopted as a general tool for the synthesis of spiroacetals for some time, with only a few reports exploiting the approach [86, 87]. Recent applications of palladium-catalyzed intramolecular alkyne hydroalkoxylation include syntheses of spirolaxine methyl ether [88] and enantiomers of the natural cephalosporoUdes [89]. 

Patil NT, Lutete LM, Wu H, Pahadi NK, Gridnev ID, Yamamoto Y. Palladium-catalyzed intramolecular asymmetric hydroamination, hydroalkoxylation, and hydrocarbonation of alkynes, J. Org. Chem. 2006 71(11) 4270 279. 

In the case of conjugated diynes, the hydroalkoxylation reaction in the presence of phenol afforded alkoxylated enyne products. Aliphatic alcohols do not add to the diyne system indicating the necessity of an acidic alcohol (phenols, naphthol or 2,2,2-trifluoroethanol). The mechanism supposed the formation of a a-cumulenyl palladium complex intermediate is consistent with the absence of the double addition of phenol to the starting diyne or the second addition of phenol to the resulting enyne [100] (Scheme 50). 

A highly active heterogeneous palladium nanoparticle catalyst for the hydroalkoxylation of 2-phenylethynylphenol was developed and employed in a continuous flow reaction system. The best of the catalyst efficiency was observed when employed in conjunction with PI1ICI2 [109] (Scheme 59). 

Camacho DH, Saito S, Yamamoto Y (2002) Anti-Wacker -type hydroalkoxylation of diynes catalyzed by palladium(O). Tetrahedron Lett 43 1085-1088... 

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