Hydroxyacetylene

Neither ground-state ethynol (hydroxyacetylene) (80) nor carbenaoxirane (81) appears to be a viable point of ingress to the oxirene-methanoylcarbene system, as both can isomerize to ketene by lower-energy pathways. The limited experimental information available on carbenaoxirane (Section 5.05.6.3.4(f/)) indicates that it is indeed largely isolated from the oxirene-methanoylcarbene manifold (but note the photolysis of ketene in Section 5.5.6.3.4(ff)) appropriate labelling experiments with (the unknown) ethynol have not been performed. 

The study of alkynylation of methyl ketones using a terminal alkyne, ZnMe2, and a salen derivative 196 as a chirality inductor provided a new method for the preparation of ct-hydroxyacetylenes (197, Scheme 112).292... 

Particularly in the cases of hydroxyacetylenes, the question "How many extractions with Et20 have to be earned out may arise. The following practical tip may be useful. Take a small (2 ml) sample from the extract with a Pasteur pipet and allow the solution to flow along a glass stopper. Further extraction is superfluous when, after the ether has evaporated, no residue is visible on the ground glass. 

Olefins, e.g., ethylene or styrene, do not displace the hydroxyacetylene from these complexes. The stability of the complexes depends on the group R. of the acetylene RMeC(OH)-C. C-C(OH)Me2 it decreases in the order R = methyl > phenyl > hydrogen. Methylation of the hydroxyl groups also lowers the stability of the complexes 36). 

When pyrolyzed, p-hydroxy alkenes cleave to give alkenes and aldehydes or ketones." Alkenes produced this way are quite pure, since there are no side reactions. The mechanism has been shown to be pericyclic, primarily by observations that the kinetics are first order" and that, for ROD, the deuterium appeared in the allylic position of the new alkene." This mechanism is the reverse of that for the oxygen analog of the ene synthesis (16-54). p-Hydroxyacetylenes react similarly to give the corresponding allenes and carbonyl compounds." " The mechanism is the same despite the linear geometry of the triple bonds. 

To explain the incorporation of alcohols and aldehydes in Fischer-Tropsch products, hydroxycarbene species M=C(H)OH were invoked by several authors although not on firm organometallic grounds (Scheme 5, mechanism ). We note particularly that metal-attached hydroxycarbene readily eliminates acetaldehyde [27] while condensation steps have not yet been seen in stoichiometric reactions. However, the first C-C bond-making step of this Anderson-Emmett-Kdlbel mechanism [28] corresponds to a hydroxyacetylene HC=C-OH species, of which metal complexes were recently isolated [29]. 

Tanaka, K., Yoshimine, M. An ab initio study on ketene, hydroxyacetylene, formylmethylene, oxirene, and their rearrangement paths. J. 

Alkynylalion of alicyclic epoxides.1 Alkynyldiethyl alanes (2 eq.) react with alicyclic epoxides (1 eq.) to form, after hydrolysis, /J-hydroxyacetylenes in fair to excellent yields ... 

Hydroperoxy-2-nitropropane, 256 p-Hydroquinone, 331,393,418 p-Hydroquinone dimethyl ethers, 432 Hydroquinones, 72 Hydrosilylation, 562 Hydroxamic acids, 204 2-Hydroximino-l-phenylpropane, 124 ai-Hydroxyacetophenone, 342 (3-Hydroxyacetylenes, 144-145 a-Hydroxy acids, 492 (5-Hydroxy acids, 301 1-Hydroxyadamantane, 126 a-Hydroxyaldehydes, 342 3o-Hydroxy-5a-androstene-17-one, 227-228... 

Some time later, Rob Guy, whose chemical skills were much respected by the research team and who was also envied for his ability to charm ladies, managed to synthesise a range of acetylene complexes of platinum. Their infrared spectra indicated that bonding of the hydrocarbon to the metal was very similar to that in olefin complexes. Interestingly, it was observed that a-hydroxyacetylenes are chelated to platinum through interaction of oxygen lone-pair electrons with a vacant 6p orbital of the metal. 

Hydroxyacetylenic acids. The dianion of propiolic acid (1) can be generated at -45° with LDA in 1 1 THF—HMPT solution. The dianion reacts with epoxides to form 5-hydroxyacetylenic acids (2) in moderate yields. The products can be converted into substituted 5,6-dihydro-2H-pyrane-2-ones, a ring... 

Ionized hydroxyacetylene (HC=C—9 ), the enol isomer of the ketene radical cation (H2C=C=0 , cannot be formed directly because 9 does not exist in... 

From the stable cation 9 it is possible to generate and study the elusive hydroxyacetylene (9) by neutralization-reionization mass spectrometry (NRMS). In a NRMS experiment (Scheme 13), mass-selected HC=C—OH" (keV domain) is first neutralized, e.g. by collisions with Xe any remaining ions are removed from the beam path by electrostatic... 

This reaction has been extended to the condensation between amidine and )0-cyano ester, amidine and )(3-hydroxyacetylene, amidine and malonate, A -vinyl amidine and acetal, and a three-component reaction of amidine with aldehyde and acetylene A ... 

In many reactions, particularly of phosphine complexes, the above reaction scheme still applies, but with a rapidly established dissociative equilibrium followed by rate-determining reaction of ML3 with Y. This is the case in oxidative elimination reactions, which are discussed in the oxidative addition section. Sometimes the mechanism and products depend on conditions, as in reaction of Pt(PPha)4 with hydroxyacetylenes, where the nature of the solvent, the presence of excess of phosphine, and particularly the stereochemistry of the alkyne, all affect the course of the reaction. ... 

The Favorsky reaction, the interaction between terminal acetylenes and carbonyl compounds in the presence of powdered dry KOH, is of limited importance for the pyrazole series, although the hydroxyacetylenic group is one of the most important protecting groups. However, most often, such an alcoholacetylenic substituent is introduced by direct alkynylation of the corresponding iodopyrazoles with... 

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