1-Ethynyl ethers

Ethynyl ethers.A synthesis from an acetic ester involves phosphorylation of the enolate [LDA (EtO)2POCl] and using f-BuLi for the elimination. 

Ethyl ethynyl ether, see Ethoxyacetylene Ethyl formate 2-Ethyl hexanol Ethyl lactate... 

The final part of this particular alkyne study108,109,144 involved the electron-rich alkynes ethyl ethynyl ether and diethylpropynylamine. Upon reaction of 221.a or 221.e with ethyl ethynyl ether, the expected adducts 247.j and 247.k were formed. Note that the electron-donating substituent is located... 

Homologues of ethoxyacetylene can be obtained by reaction of the metallated ethynyl ether in liquid ammonia with primary alkyl bromides and iodides 167]. Because of their better solubiliiy, the lithium compounds are preferred over their sodium and potassium analogues, lithium ethoxyacetylide is generated from the readily accessible 2-bromovinyl ethyl ether and two equivalents of lithium amide. This starting compound is obtained as a mixture of the E-and Z-isomer. When this mixture is heated with powdered KOH, only the Z-isomer is converted into ethoxyethyne. Alkali amides are able to conven both isomers into ethoxyethyne and its alkali compounds. A possible explanation for this violation of the "rule of... 

Ethynyl ethers react (slowly) with aqueous ammonia [24],... 

The fact that allyltributyltin and styrene which are electroneutral were successfully added to PCTFE led us to the question "Can electron-rich or electron-poor trapping agents be used ". The electron-rich agents that we examined were ethyl ethynyl ether and ethyl vinyl ether. On the side of the electron-poor alkenes, eight were investigated ethyl acrylate, methyl methacrylate, methyl vinyl ketone, acrylonitrile, methacrylonitrile, vinyl bromide, chloromethyl styrene, and 4-vinylpyridine. The details of each reaction are summarized. 

In the case of the electron rich reagents, no addition products were observed, either under catalytic or stoichiometric conditions. In all cases, no evidence of incorporation was discerned from IR analysis. In addition to unidentifiable materials (in the ethyl ethynyl ether case), substantial side reaction could be recognized. 

A neat hydroformylation - allylboration - hydroformylation reaction sequence reported by Hoffmann el al. afforded the pyrano-fused oxepanes 135 and 136 (48% total yield ca 1 1 ratio) from the precursor 134 the compound 134 required a number of steps for synthesis from the alcohol 130, the ethynyl ether 131, and the boronate 133 (by addition of 132) in moderate overall yield. Dess-Martin oxidation of 135 and 136 then afforded the final lactones 137 and 138 [01NJC102],... 

In contrast to the major course of addition in ethynyl ethers, the predominant mode in ethynyl thioethers is nucleophilic attachment to Cp, as in equation (40). . . Arens accounted for such differences in orientation by proposing that... 

Neither the Viehe nor the Arens routes to the ethynyl ether are plausible for this system. The l-phenyl-l-methoxy-2-haloalkenes of equation (259), for example, may be recovered intact when treated in MeOH with 4m NaOMe at 155 °C . Though these conditions are presumably suitable for the generation of or C vinyl anions, no onium process (equation 253) seems to have occurred. Further, it seems improbable that phenylacetylide could be a precursor of the ethynylether (Arens mechanism), since this ion abstracts protons from protic solvents (/r lO M s at 25 °C in water) and halogen from hypohalite (OX") [k(Cl) = 2-3 x IQ- m" s" at 25 °C in water] . Thus, the possibility that there is an Arens ion-molecule intermediate, which can survive long enough in methanol to rearrange and form the alkynyl ether... 

Another reason to support the IIT mechanism and discount the other two routes to the ethynyl ether is the element effect observed in the formation of this product, A (CI)/k(Br) = 1-2 (Table 27). Attacks at X or Q do, in fact, yield element effects < 1 while attack at C gives a value > 1. 

Difficulties arise when process (2) is carried out in the presence of mobile protons. This stems from the fact that carbanionic intermediates such as those shown in Scheme 6 are the precursors to the substitution product. Interception of these intermediates by proton traps may prevent the formation of the desired product or at least diminish its yield. Moreover, process (2) proceeds more rapidly in the presence of an aprotic solvent than a protic solvent. This is well illustrated in the synthesis of ethynyl ethers . When methanol is used as the solvent in equation (277), the... 

Activation by addition of a carboxylic acid to a triple bond occurs with ethyl ethynyl ether,which forms amides via reactive enol esters. The reaction is catalyzed by mercury(II) oxide under almost neutral conditions. Push-pull alkynes exert higher reactivityThe intermediate enol esters (Scheme 4) rearrange and react with the amino function of a second amino acid. Hydroxy, thiol and imidazole functional groups do not have to be protected. The degree of racemization is low, and yields are good in the case of small peptides. 

Synthetic uses. Arens,° in reviewing the many reactions of ethynyl ethers and thioethers, states that the first use of ethoxyacetylene for the synthesis of a,/3-unsaturated aldehydes was described in a paper published in Russia in 1945, but that the paper was abstracted incorrectly and remained unknown in the western world, van Dorp and Arens" rediscovered the method and in 1947 described its use in the synthesis of vitamin A aldehyde. Ethoxyacetylene is treated with ethyl-magnesium bromide to form the Orignard reagent, and this is added to the carbonyl group of the "C lii-kelone" to produce the acetylenic cnrbinol (I). Semlhydrogenation... 

Examination of the isodesmic reactions used below for the calculation of the enthalpies, (see Table 3.6) reveals that accurate enthalpies for a number of vinyl and ethynyl ethers and alcohols are needed so they can be used as reference species. Enthalpies of the species, which were not found in the literature, were calculated as well with DFT combined with isodesmic reactions. To validate the accuracy of the data for reference species, they were also estimated... 

TBAF tetra-n-butylammonium fluoride TMSEE (trimethylsilyl)ethynyl ether... 

---