Acetylenic ethers, preparation

Unsaturated esters can be prepared from the corresponding acetylenic ethers with yields in most cases of >50% (91) as in the following example ... 

Tetraphenyltellurophene To a suspension of 1,4-dilithiotetraphenyl-l,3-butadiene in 100 mL of ether, prepared from 10 g (56 mmol) of diphenyl acetylene and excess of lithium, is added over 15 min a solution of TeCl4 (5.3 g, 19.7 mmol). The green mixture is poured into a mixture of CH2CI2 and water, the organic phase is separated, filtered through anhydrous MgS04, filtered and evaporated. The residue is recrystallized from dichloromethane/ethanol, giving tetraphenyltellurophene 5.35 g (56%), m.p. 239°C. 

Zinc enolate 4, prepared from acetylene ether pyridine i-oxide, mercuric chloride, and zinc, adds to aldehydes to form a-chloro-3-hydroxy esters 5 in good yields ( ). Subsequent treatment with base gives trans-epoxyesters, one of which 6 is converted to 2-amino-2-deoxy-D-ribose stereoselectively in good yields (O. 

General Method for Preparation of Ynamines by Reaction of Acetylenic Ethers... 

Difficulties arise when the most simple ynediamine bis(dimethylamino)acetylene is prepared starting with trichloroethylene since dimethylamine may react further giving tris(dimethylamino)ethylene 163). A simple one-pot procedure for this ynamine has been elaborated in which trichloroethylene is treated with sodium amide and dimethylamine under normal pressure. The average yield is about 60 %163). Di-chloroacetylene ether complex can now be prepared under phase-transfer (PT) conditions from trichloroethylene. It reacts with dimethylamine under PT conditions to N,N,N"N -tetramethylglycinamide apparently via the ynediamine intermediate 164). 

ACETYLENIC ETHERS FROM ALCOHOLS AND THEIR REDUCTION TO Z-AND E-ENOL ETHERS PREPARATION OF 1-MENTHOXY-1-BUTYNE FROM MENTHOL AND CONVERSION TO (Z)-AND (E)-1-MENTHOXY-1 -BUTENE ([Cyclohexane, 2-(1 -butynyloxy)-4-methyl-1 -(1 -methylethyl)- [1S-(1a,2p,4p)]-], end [[[Cyclohexane, 2-(1-butenyloxy)-4-methyl-1-(1-methylethyl)-, [1S-[1a,2P(Z),4p]]- and [lS-[1 ,2p(E),4P]]-)... 

ACETYLENIC ETHERS FROM ALCOHOLS AND THEIR REDUCTION TO Z- AND E-ENOL ETHERS PREPARATION OF 1-MENTHOXY-1-BUTYNE FROM MENTHOL AND CONVERSION TO (Z)- AND (E)-1 -MENTHOXY-1 -BUTENE... 

Acetylenic Ethers from Alcohols and Their Reduction to Z- and E-Enol Ethers Preparation of 1-Menthoxy-1-butyne from Menthol and Conversion to (Z)- and (E)-1-Menthoxy-1 -butene. 

Unsaturated ethers, RCH = CHCH20CHj, have been prepared from the corresponding allylic alcohols and dimethyl sulfate in the presence of sodium amide (60-80%). Acetylenic ethers are made in a similar manner from acetylenic alcohols. The hydroxyethylation of phenols with ethylene sulfite or ethylene carbonate appears to be a promising reaction for the formation of hydroxy ethers of the type ROCH,CHjOH. ... 

Alkynylation of zinc-copper compounds has been used for the synthesis of polyfunctional acetylenic ethers [84] and for the preparation of building blocks for pharmaceutically active compounds [85]. Whereas cross-coupling between non-activated iodoalkenes and zinc-copper reagents only proceeds at elevated temperatures and in polar solvents such as NMP or DMPU (60 12 h) [86], alkenyl... 

Polyfunctional zinc-copper reagents react efficiently with 1-bromo- or I-iodoaUcynes furnishing functionalized alkynes in good yields. The reaction proceeds at low temperature (—65 °C to —55 °C) and has been applied to the preparation of pheromones (Scheme 9-23 [53]) and polyfunctional acetylenic ethers [54]. 

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. 

Alkali hydroxides are used without a solvent186 for preparation of acetylenic ethers from alkoxy- or aryloxy-bromoethylenes, e.g., of phenoxyacetylene from 1 -bromo-2-phenoxyethylene 187... 

Acetylenic ethers and esters represent an important class of functionalized acetylene derivatives of the hypothetical alkynols, RC=COH. The chemistry of acetylenic ethers has been well developed since their first preparation about 100 years ago Several exhaustive reviews covering the literature on acetylenic ethers and their analogs up to 1985 have been published in the last 30 years. In contrast to acetylenic ethers, esters of alkynols were unknown until the mid-1980s when the first preparation of alkynyl tosylates was reported. In the following years a wide variety of alkynyl carboxylate, phosphate and sulfonate esters has been prepared from alkynyl iodonium salts. The chemistry of these novel derivatives of alkynols has been summarized in a recent review. In the last 10 years considerable interest and research activity has arisen toward alkynols themselves and such derivatives as alkynolate salts and silyl ynol ethers. The present chapter will cover the chemistry of acetylenic ethers and esters as well as related derivatives of ynols with emphasis on new developments in this subject during the last 5-10 years. 

The most general and well-developed procedures for the preparation of acetylenic ethers are based on dehydrohalogenation or dehalogenation of various haloacetals (for example, acetals of chloroacetaldehyde 52) or haloalkenyl ethers 53 (equation 34) . The first product in these eliminations usually is alkoxyacetylide 54 which can be subsequently quenched with a variety of electrophiles such as water, alkyl halides, ketones, etc to give the final product 55. 

Dehydrohalogenation or dehalogenation of haloalkenyl ethers is probably the most universal approach to alkoxyacetylenes . During the last 10 years this approach has been significantly improved and applied to the preparation of various acetylenic ethers. In contrast to older procedures, in which NaOH or NaNH2 are used as bases, these new methods usually employ alkyllithium or potassium hydride. In 1985 Smithers" " developed a procedure based on the reaction of a-chloro-jS,j5-dibromovinyl ethers 59 with butyllithium (equation 36). In contrast to previous methods, the first step of this reaction is metallation... 

The parent alkoxyacetylenes, HC=COR, are the most readily available representatives of acetylenic ethers. Moreover, ethoxy acetylene is even commercially available, and can generally be easily prepared by standard, well developed, procedures . These compounds can usually be further functionalized by standard methods employed for terminal alkynes. 

The most general approach to the preparation of functionalized acetylenes including acetylenic ethers involves elimination techniques, mostly dehydrohalogenation of appropriate olefin precursors (see Sections II.D.l and III.A.l). However, these and related procedures do not work for the preparation of alkynol esters 94-96, and this undoubtedly is one of the major reasons why these compounds remained unknown until the mid-1980s4 5. 

J.F. Arens, The chemistry of acetylenic ethers XIII. Acetylenic ethers as reagents for the preparation of amides. Rev. Trav. Chim. Pays. Bas. 74 769-770 (1955)... 

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