Hydroalkoxylation of alkyne

A few examples have recently appeared in the literature where epoxides can function as nucleophiles for the hydroalkoxylation of alkynes. Both AuC 353 and HgO354 in an acidic medium have been used as catalysts for this purpose (Equation (100)). 

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]. 

Transition metal-catalyzed addition of heteroatom-hydrogen bonds to alkynes in syntheses of cyclic amines and pyrroles by hydroamination reactions, in syntheses of O-heterocycles by hydroalkoxylation of alkynes, and in syntheses of S- and Se-heterocycles 04CRV3079. 

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... 

Gold-catalyzed organic reactions, particularly, olefin epoxydation and hydroamination or hydroalkoxylation of alkynes to give N- or O-het-... 

Representative procedure for the gold-catalyzed hydroalkoxylation of alkynes. Trans-2,5-dimethyl-2,5-dimethoxy-l, 4-dioxane ... 

A gold-catalyzed benzylic C-H functionalization for the synthesis of IH-isochromene derivatives 34 was disclosed by Hashmi and coworkers in their study of the intramolecular hydroalkoxylation of alkynes (Scheme 12.15) [19]. A proposed mechanism for this reaction is shown in Scheme 12.16. The reaction... 

The hydroalkoxylation of alkynes has recently attracted some marked interest. Several groups have developed alkyne alkoxylation/Claisen rearrangement tandem processes using allylic alcohols as nucleophiles and NHC-Au complexes as the catalysts. The group of Nolan developed, in 2013, the hydrophenoxylation of alkynes by using a cooperative NHC-Au catalysis pro-cess. The hydroalkoxylation of allenes could also be performed. This reaction was shown to proceed in a regioselective manner with the alcohol being introduced on the least hindered terminal carbon of the allene. ... 

There was an explosion of work described on gold(I) and gold(lll) catalysis in the early 2000s, and its appUcatiOTi in the hydroalkoxylation of alkynes was no exception [90, 91]. Beginning with studies toward Au(l)- or Au(lll)-catalyzed synthesis of bridged acetals [92], these catalysts were soon applied to the synthesis of spiroacetals [93, 94]. This method has been widely embraced by the synthetic conununity and used in the syntheses of a variety of complex spiroacetal namral products, including the cephalosporoUdes [95], okadaic acid [96], and ushikulide A [97]. 

Ramana et al. [89] opted for a Pd(II) catalyst for the intramolecular hydroalkoxylation of alkyne 186 in their synthesis of the enantiomeric cephalosporolides 189a and 189b (Scheme 44). The spirocyclization afforded a 1 1 mixture of the spiroacetals 187, which were then elaborated to the ent-natural products via hydrolysis of the isopropylidene acetal, followed by oxidation and Barton-McCombie deoxygenation. 

Scheme 34 Heterobimetallic cluster catalyst for hydroalkoxylation of alkynes...

Few reports are known for hydroalkoxylation of alkynes compared to hydroamination partly due to the diminished nucleophilicity and the weaker... 

Messerle BA, Vuong KQ (2007) Rhodium- and iridium-catalyzed double hydroalkoxylation of alkynes an efficient method for the synthesis of O, 0-acetals catalytic and mechanistic studies. Organometallics 26 3031-3040... 

Gold-Catalyzed Hydrofunctionalization of Ti-Bonds 2.1 Hydration and Hydroalkoxylation of Alkynes... 

Intermolecular hydroalkoxylation of alkynes is also possible by hydration of propargyl acetates assisted by a neighboring carbonyl group [140] and with A -Boc-protected carbamates [141]. 

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