Abstract hydrozirconationzr zn transmetalationaldimine addition. A functionalgrouptolerant catalytic trans hydrogenation of. Like hydroalumination and hydrozirconation, hydroboration of alkynes also provides a convenient and stereospecific route to alkenyl metal reagents. Secondary reactions are nucleophilic additions, transmetalations, conjugate additions, coupling reactions, carbonylation and halogenation. Alkenes also called olefins and alkynes also called acetylenes belong to the class of unsaturated aliphatic hydrocarbons. Hydrozirconation products can be used directly as carbanion equivalents, but such reactions are generally not highly successful. The zrzn transmetalation, aldehyde addition methodology developed in the wipf group was extended to the synthesis of allylic amines. Buzrcp2cl generated in situ by treatment of cp2zrcl2 with t. Organozirconium derivatives, obtained by hydrozirconation of alkynes, usually possess insufficient reactivity for use in crosscouplings, most likely due to the bulkiness of the cp 2 zr residue, but are very useful as intermediates for the generation of organozinc compounds section 9. Myers hydrozirconation and carbozirconation chem 115 ch 3lizncl 2 reverses the regioselectivity in hydrozirconation of propargylic alcohols. Alkyne definition is any of a series of openchain hydrocarbons cnh2n2such as acetylene having one triple bond. This metallocene is used in organic synthesis for various transformations of alkenes and alkynes.
Regioselective alkylzirconation of internal alkynes. Ethyne is used as the basic material for making many other organic compounds such as ethanoic acid, ethanal, acrylic acid, etc. Homopropargylic alcohols undergo directed hydrozirconation with schwartz reagent cp 2 zrhcl to generate vinylmetal species in which the metal fragment is proximal to the alkoxide. Alkynes are traditionally known as acetylenes, although the name acetylene also refers. We learned about hydrogenation when we first checked out addition reactions, but we were doing that with alkenes. Acetylene itself is formed from the reaction of the inorganic compound calcium carbide with water. Hydrozirconation of alkenes and alkynes, followed by insertion of 1halo1lithio1alkenes, generated in situ by lithium tetramethylpiperidide deprotonation of vinyl halides, affords. The authors propose that alkoxide generation with ch 3li promotes directed hydrometalation, while zncl 2 blocks isomerization to the thermodynamically favored linear vinylzirconium species. Hydrozirconation of alkenes and alkynes researchgate. Using this method, terminal and internal alkynes can be synthesized. Some of the important methods of preparation of alkynes are. This method is suitable for a wide range of organic halides and alkenes with excellent functional group tolerance, suggesting. A convenient procedure for hydrozirconation of alkynes with i.
Described herein is the carbometallation of unsymmetrically 1,2disubstituted alkynes with alkylzirconocene complexes, which are generated by hydrozirconation of alkenes. Under standard hydrozirconation conditions, terminal propargylic alcohols are no exception. Different energy and geometry changes may be required for additions to an alkyne and an alkene so some surprising outcomes may occur with alkynes. Hydrozirconation has recently been developed as a procedure for functionalizing alkenes, alkynes, and 1,3. The ionic liquid and palladium catalyst can be recycled at least six times. The hydrozirconation reaction describes the reaction of an olefin alkene with cp 2 zrhcl, a, which is commonly referred to as schwartzs reagent. Methods of preparation of alkynes by dehydrohalogenation. A poisoned catalyst will permit the reduction of a triple bond to a double bond by syn addition, but no further. Nphosphinoyl, nsulfonoyl, and ncarbamoylimines were excellent substrates for this transformation. A convenient procedure for hydrozirconation of alkynes with iso. The adduct is the sole product of the coupling of vinyl. Myers hydrozirconation and carbozirconation chem 115. The main preparative reactions involve the elimination of groups or ions from molecules, resulting in the formation of.
Hydrozirconationzrzn transmetalationaldimine addition. Under mild conditions, elimination with sodium amide in ammonia, for example, takes place at. This hydrozirconationtransmetallation sequence provides a route to net hydroalumination of alkenes and alkynes. The first three members of alkyne family ethyne, propyne and butyne are colourless gases, the next eight members are liquids and the higher ones are solids.
The first example of hydrozirconation of alkynes in room. The hydrozirconation of terminal alkynes proceeds rapidly 515 min at room temperature in ch2cl2 or thf, and is very easily monitored visually since cp2zrhcl is insoluble in most organic solvents whereas the colored organozirconocenes 4 are highly soluble. Ethylene and acetylene are synonyms in the iupac nomenclature system for ethene and ethyne, respectively. The loss of a hydrogen atom and a halogen atom from adjacent alkane carbon atoms leads to the formation of an alkene. These compounds are slightly soluble in polar solvents and are.
Addition to internal alkynes often displays lower selectivity, but the initial kinetic distribution of products can reach equilibrium via ahydride elimination from a. This isomerization occurs through a series of betahydride elimination and olefin insertion reactions as shown below. Hydration and hydroamination of 1alkynes with ruthenium. Hydration of 1alkynes to aldehydes the addition of water to alkynes with hgii salts to form carbonyl compounds was. A diverse set of terminal alkynes underwent rapid and mild hydrosilylation in the presence of cprumecn 3pf 6 to give 1,1disubstituted avinylsilanes in good to excellent yield, often with low catalyst loadings scheme 2, table 1. This pdf receipt will only be used as the basis for generating pubmed central pmc documents. Since highersubstituted alkyl alkynes internal alkynes are more stable than terminal alkynes hyperconjugation, isomerization is favored thermodynamically. Except for ethyne, which has characteristic smell, all members are odourless. Schwartzs reagent is the common name for the organozirconium compound with the formula. These intermediates react with a variety of electrophilic reagents to give organic products in high yield. Hydrozirconation of terminal alkynes with cp2zrhcl schwartz reagent usually proceeds with high selectivity to yield the terminal vinyl zirconium. The acidity of alkynes, nonpolar bonding strength, and linearity is due to the triple bonds in these compounds.
Directed hydrozirconation of homopropargylic alcohols. The uniqueness in the alkyne structure is due to the hybridization. Since isomerization of organozirconocenes is generally faster than hydrozirconation, the thermodynamically most stable, e. For 2octene, for example, this results in the exclusive formation of 1metalated compound ref. This group of compounds is a homologous series with the general molecular formula of c n h 2 n 2, where n equals any integer greater than one. Ethyne is used for preparing starting material for many useful polymers. Zirconium and palladium catalyzed telescopic synthesis of.
The reaction is tolerant to a wide range of functional groups including halogens, free alcohols, alkenes, internal alkynes, esters, and. So were going to start with a terminal alkyne over here. This method was once an important industrial process for the manufacture of acetylene. In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carboncarbon triple bond. Alkylzirconium complexes react with acetyl chloride to give methyl ketones scheme 10, 28 but yields are not always good and alkenyls do not react. Hydrozirconation of readily available alkynyldioxaborolanes gives access to 1,1bimetalloalkenes, which can be used to synthesize trisubstituted alkenes. A convenient procedure for hydrozirconation of alkynes with isobuzrcp2cl generated in situ by. Directed hydrozirconation of homopropargylic alcohols ncbi nih. The use of toluene as a reaction solvent was required to obtain high yields and low reaction times. Rs and rl represent small and large substituents, respectively. Alkynes are hydrocarbons, which are organic chemical compounds containing carbon c and hydrogen h atoms, and the feature that makes them. However, standard catalysts like pdc will not allow hydrogenation to stop before the alkane stage.
You can see theres a hydrogen on one side of our alkyne. Alkenes are hydrocarbons that contain a carboncarbon double bond, whereas alkynes have a carboncarbon triple bond. Visiblelightinduced nickelcatalyzed crosscoupling with. Schwartzs systematic investigation 1974 of hydrozirconation of alkenes and alkynes with cp. Alkynes are hydrogenated in generally the same way as alkenes. However, initial attempts to achieve palladiumcatalyzed crosscoupling of alkenylboranes with alkenyl halides were unsuccessful, due to the poor carbanionic character of these reagents. Ketones can be synthesized from acid halides and alkenes or alkynes.
So were going to add water, sulfuric acid, and mercury ii sulfate to our alkyne. Christopher kendall, phd university of pittsburgh, 2004 the zrzn transmetalation, aldehyde addition methodology developed in the wipf group was extended to the synthesis of allylic. And on the other side of our alkyne, lets say its an alkyl group, bonded to this carbon on the right. Hydrocarbon hydrocarbon nomenclature of alkenes and alkynes. Unusual regioselectivity in the reductive coupling of. A convenient procedure for hydrozirconation of alkynes. Higher alkenes and alkynes are named by counting the number of carbons in the longest continuous chain that includes the double or triple bond and appending an ene alkene or yne alkyne suffix to the. Physical properties of alkynes are very similar to the physical properties of alkenes. Ethyne is prepared on large scale by the reaction of water on calcium carbide. Addition of water to the second step deactivates the zirconocene catalyst, which is otherwise deleterious to crosscoupling. Ethyne can also be prepared on industrial scale by pyrolysis of methane at very high temperature of about 1800 k. Alkynes are used in the preparation of many other compounds. Calcium carbide is prepared by heating quicklime with coke. Treatment of alkenes and alkynes with zirconocene hydrochloride gives rise to alkyl and alkenylzirconium intermediates, respectively.
Substrates for hydrozirconation are alkenes and alkynes. The zirconium compounds are formed in situ from alkynes and allenes, and the overall reaction opens a new preparative route to the vitamin e side chain through asymmetric induction in the 1,5. The preparations of alkynes are very similar to those of the alkenes. Avoiding isolation of intermediates saves time and reduces waste.
However, we report that the sense of regioselectivity is completely reversed when the hydrozirconation is performed on the lithium. The in situ conversion of alkenes and alkynes into chainextended synthetic building blocks by sequential hydrozirconation and further metalcatalyzed or metalmediated condensations with electrophiles is thus characterized by experimental convenience and considerable strategic flexibility. With terminal alkynes the terminal vinyl zirconium product is predominantly formed. The regio and stereochemistry of the alkene is set by initial hydrozirconation of the alkyne. A general visiblelightinduced single nickelcatalyzed crosscoupling method with alkylzirconocenes has been developed. Alkylzirconocenes are generated in situ from terminal or internal alkenes through hydrozirconation and chain walking. Electrophilic trapping yields trisubstituted olefins in good yields with good control of regio and stereochemistry. Hydrozirconation and its applications springerlink. Physical properties of alkynes chemical properties alkynes. In praxis, the reaction is carried out with moderately strong bases, e. Molecular and structural formulas the alkynes comprise a series of carbon. The uses of ethyne, the first member of alkynes are listed below.
Likewise, all the known addition of water to terminal alkynes reported thus so far using hgii. Schwartzs reagent is the common name for the organozirconium compound with the formula c 5 h 5 2 zrhcl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after jeffrey schwartz, a chemistry professor at princeton university. In this reaction the insertion of either a terminal or internal olefin gives the same product, b. Hydrocarbon nomenclature of alkenes and alkynes britannica. For instance, whereas hydrozirconation of dodecyne proceeded rapidly and quantitatively in the absence of zncl2, we observed pdf available in journal of the serbian chemical society 693 march 2004 with 22 reads. Alkenes are characterized by the general molecular. Piyasan praserthdam, suphot phutanasri and jumpot meksikarin, catal. Addition of water to the second step deactivates the zirconocene catalyst, which. A convenient procedure for hydrozirconation of alkynes with isobuzrcp2cl generated in situ by treatment of cp2zrcl2 with tertbutylmagnesium chloride. A new, highly efficient in situ protocol cp 2zrcl 2 lialhobut 3 is described for the generation of the schwartz reagent which provides a convenient method for the amide to aldehyde reduction and the regioselective hydrozirconation iodination of alkynes. Cbr 4, pph 3 k 2co 3 68% yield tbso br br 5 mol% pdpph 3 2cl 2 10 mol% dibal tbso zrcp 2cl tbso br tbso tetrahedron. Double elimination of 1,1 or 1,2dihalogen alkanes with strong bases yields the corresponding compounds with triple bonds. Alkenylzirconium species from hydrozirconation of terminal alkynes also transmetallate ef.
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