Addition of alcohol to alkynes

Gold(I) complexes of the type [AuCl(PPh3)ra] (n= 1, 2) or [Au(N03)(PPh3)] show an excellent performance towards oxidative addition carbonylation or aromatic amines to form corresponding carbamates, and also towards the carbonilation of aliphatic amines to produce either alkylureas or formamides.2552,2553 Cationic gold(I) compounds of the type [AuL]+ where L = phosphine, phosphite, or arsine are excellent catalysts for the addition of alcohols to alkynes.2554... 

The gold(i)-catalyzed addition of alcohols to alkynes has been investigated in the gas phase by mass spectrometry techniques. While in the condensed phase, an efficient coupling to the corresponding enol ethers has been observed, in the... 

In chronological order, the next milestones in research were the studies by Fukuda and Utimoto on the addition of nucleophiles (water, alcohols and amines) to alkynes [13]. A decade later, Teles obtained notable turnover numbers (TONs) and turnover frequencies (TOFs) in the addition of alcohols to alkynes [14]. 

Until 1998, only gold(III) was believed to be effective for catalyzing these processes because, as mentioned previously, only the gold(I) compound K[Au (CN)2] was tested and it was inert to catalysis. Fortunately, Teles et al. reported very strong activity in the addition of alcohols to alkynes when they used cationic gold( I) -phosphane complexes [14]. In this study, the aforementioned authors tested for the first time the suitability of nucleophilic carbenes that displayed even greater activity than other gold complexes, but they were unable to synthesize the subsequent cationic derivatives. 

The addition of alcohols to alkynes is catalyzed by bases,411,412 or salts of palladium,413 silver414 or mercury413 (equations 254-256). The mercury-catalyzed processes are summarized in the following section. 

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],... 

The status for homogeneous catalysis by gold in solution was dramatically transformed in 1998 by the results of Teles et al.11 This BASF group described the use of cationic Au1 complexes of the type [L-Au+] (where L is a phosphane, phosphite or arsine) for the addition of alcohols to alkynes in the presence of a Lewis or Brpnsted acid as a co-catalyst in methanol at 313 K. An example of such a reaction is the conversion of 3-hexyne to 3,3-dimethoxyhexane ... 

Intermolecular additions of alcohols to alkynes can be coupled with other tandem reactions of the alkenyl-gold intermediate. Thus, reaction between salicylaldehyde and phenylacetylenes can give access to the isoflavanone skeleton (equation 7), whereas a three-component addition of methylenecylopropylcarbinols, arylalkynes, and alcohols leads to bicyclic compounds (equation 8). ... 

In contrast to the addition of water, the addition of alcohols to alkynes leads to stable enol ethers. Those of economic importance are almost exclusively the vinyl ethers prepared from acetylene. This preparation is carried out under base catalysis [41] (KOH, alcoholates, and the like). The noble metal-catalyzed alcohol addition does in fact likewise lead, in an intermediate stage, to vinyl ethers, but these react under the prevailing conditions, generally in a quantitative reaction, to give to corresponding acetaldehyde dialkyl acetals [42]. This is illustrated in (eq. (18)), which takes as its example the addition of n-butanol to acetylene in the presence of Na2PtCl6. 

The nucleophilic addition of alcohols to alkynes was reported by Utimoto with NaAuCU and later by Teles with cationic gold complexes.The enol ethers formed can be hydrolyzed to form carbonyl compounds or trapped as ketals (equations 4 and 5). An intramolecular version of this reaction was reported by the group of Genet to give bicyclic ketals (equation On the basis of this concept, a glycosidation... 

A useful method for access to vinyl ethers involves the addition of alcohols to alkynes in the presence of 18-crown-6. The (Z)-isomers are predominant. 

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... 

Cationic gold(I) complexes Highly efficient catalysts for the addition of alcohols to alkynes, J. H. Teles, S. Brode, and M. Chabanas, Angew. Chem. Int. Ed., 1998, 37, 1415. 

Among many methods, the addition of alcohol to alkyne is a potential method of choice to prepare vinylethers [101]. However, even though the addition of methanol to electron-deficient alkynes such as acetylene dicarboxylates is easy, the intermo-lecular addition of alcohol to unactivated alkynes in the presence of metal catalysts is not straightforward. With ruthenium catalysts, the only reported examples concern the addition of allylic alcohols to terminal alkynes. Thus, in the presence of a catalytic amount of RuCl(tris(pyrazolyl)borate)(pyridine)2, allyl alcohol adds to phenylacetylene in refluxing toluene to produce a 1 1 mixture of allyl (3-styryl ether and 2-phenylpent-4-enal (resulting from Claisen rearrangement) in 72% overall yield. (Scheme 22) [86]. 

A study on the intermolecular addition of alcohols to alkynes in the presence of Pt (11) (as Zeise s dimer or as simple dihalide salt) has been repotted by Hartman in 2004 [144]. The proposed reaction mechanism parallels the hydration mechanism shown in Scheme 65. However, the nucleophilic addition, shown in step 2, is reversible when tautomerism to a carbonyl is not available, which would be the case if alcohol was the nucleophile. Thus, if alcohol is used as the nucleophile, the initial product would be a platinum-bound protonated vinyl ether in the equilibrium shown in Scheme 80. Since tautomerism is not possible for this species, then the addition of an appropriate base could abstract the acidic proton from the intermediate and drive the equilibrium forward. 

Scheme 80 Proposed mechanism for Pt(II) catalyzed inlermolecijlar addition of alcohols to alkynes...

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