Transient intermediates of the tebbe reagent intercepted and characterized by atmospheric pressure chemical ionization mass spectrometry. Examples of how to accomplish specific tasks in a reagent webapp. A guide to solvents and reagents in introductory organic chemistry. The tebbe reagent and the petasis reagent share a similar reaction mechanism. Feb 11, 2016 exploratory chemistry research in us industry. The alkene must then however react with more tebbe reagent or more schrock carbene to form a metallacyclobutane. The tebbe s reagent is the organometallic compound with the formula c 5 h 5 2 tich 2 clal ch 3 2. Transient intermediates of the tebbe reagent intercepted and. Tebbe olefination petasis alkenylation springerlink. Chemistry reagent manual prepared by chemistry department, sgtb khalsa college page 5 under dbts star college scheme 23. Titanium reagents for the alkylidenation of carboxylic. The petasis reagent is also very air stable, and is commonly used in solution with toluene or thf. Tebbe first isolated the titanocenealuminum complex in 1974.
Pushing electronswhich carbene ligand for which application. Subsequent c1incorporation using tebbe reagent, formation of a cyclic carbonate, and deprotection of the two isopropylidene ketals afforded tetrol 4 which, upon treatment with phenylselenyl triflate, was stereoselectively cyclized in a 6exotrig selective manner. Mechanism of olefination via titaniumcarbenes the most thorough mechanistic study on tibased olefination has been done using the petasis reagent. The originally proposed mechanism 3 was very different from that of tebbe olefination. Unlike the simmonssmith reagent, it olefinates ester and amide carbonyl functions, as well as aldehydes and ketones. From toothpaste to tebbe reagents, michael tarselli takes a look at the many different faces of titanium. Carbonyl methylenation and alkylidenation using titanium. Organometallics are useful reagent, catalyst, and precursor materials with applications in thin film deposition, industrial chemistry, pharmaceuticals, led manufacturing, and others. The related titanium metallacycles, which are prepared from the tebbe reagent and an alkene in the presence of a lewis base, accomplish similar alkylidenations. The reagent can be used for the methylenation of not only aldehydes and ketones, but also esters, lactones, amides, and thioesters, which cannot be achieved by the wittig reagent.
Structural elucidation of the illustrious tebbe reagent. Shop online for a wide selection of tebbe reagent, 0. Wittig reagents are triphenyl phosphonium ylides and are strong bases. Files are available under licenses specified on their description page. Carbenes and carbene complexes i introduction a very interesting honest class of radicallike molecules steadily becoming more important as they find far more synthetic applications we will. Summary of the tebbe reagent tebbe methylenation of esters has been accomplished in the presence of many functional groups. The film recounts the story of operation entebbe, a 1976 counterterrorist. Transient intermediates of the tebbe reagent intercepted and characterized by. The tebbes reagent is the organometallic compound with the formula c5h52tich2clalch32. Mild methylenation reagent of carbonyl compoundspetasis. The active olefinating reagent, cp 2 tich 2, is generated in situ upon heating. The tebbe reagent has been renowned for decades for its utility as a methylenetransfer reagent.
Transient intermediates of the tebbe reagent intercepted. Treatment of ketones with excess tebbe reagent stack exchange. The tebbe reagent will methylenate aldehydes and ketones without epimerization at achiral centers, as illustrated in eq 2. For instance, it is not possible to convert an ester or lactone using tebbe or wittigtype reagents. Synlett tebbes reagent spotlight 204 thieme connect. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing. These results prompted us to investigate the reactions of tebbe reagent with some carbonyls carrying better leaving groups. Peterson reagents, in which alkyloxy groups on the silicon atom fix the conformation of the anion after treatment with libase, were reacted with a variety of aldehydes to give z. It was originally synthesized by fred tebbe at dupont central research. He did most of the construction himself and built it on land that his father had given him when he married my mother faye. Please note that all enquiries should relate specifically to european journal of soil biology.
C bond cleavage via c, gave an unsatisfactory yield. The tebbe s reagent is the organometallic compound with the formula c 5 h 5 2 tich 2 clalch 3 2. In 1978, tebbe reported that a complex prepared by reaction of titanocene dichloride with trimethylaluminum could transform esters into the corresponding vinyl ethers in moderate yields 22, 23. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the r2co group into the related r2cch2 derivative. Mckiernan department of chemistry, university of glasgow, glasgow, uk g12. Furthermore, the tebbe reagent was also found to methylenate aldehydes and ketones, sometimes more effectively than the wittig method. Olefination of carbonyl functions may be effected by tebbe s reagent, which is the source of a tiiv methylene complex.
Finally, the most frequently used strategy for formal hydromethylation of ole. Research has focused for many years on the development of carbon atom transfer reactivity after fischers discovery of heteroatomstabilized nucleophilic carbene complexes. Fred tebbe, 1976, the tebbe reagent in 1980 grubbs uses the tebbe reagent and isolates. Tebbe s reagent act to methylenate carbonyl groups.
The tebbe reagent 3 thus formed is used in situ by cooling the mixture in an icewater bath note 4, then adding 4. The tebbe s reagent transfers a methylene group ch2 efficiently to various carbonyl compounds to afford olefins. Tebbe reagent is one of numerous organometallic compounds sold by american elements under the trade name ae organometallics. Lombardos reagent, and several similar organotitanium compounds e. The tebbe reagent is a methylidene transfer reagent. The key advantage of the tebbe reagent over other titanium reagents used in alkylidenations is that the reactive titanium methylidene is generated and reacted at low temperature. This category was created to provide a home for inorganic compounds such as nabh 4 that are widely used in stoichiometric quantities in organic chemistry, but widely used organic reagents such as. Spotlight 204 this feature focuses on a reagent chosen by a postgraduate, highlighting the uses and. Alkenes including dienes, vinyl fluorides, vinyl chlorides, aryl bromides, and aryl iodides ethers including benzyl,and trityl ethers, silyl ethers including tms,tbdms,and ditertbutylsilylene. Acroseal glass bottle packed in tin can tebbe reagent, 0.
Aluminum is the most abundant metal in the earths crust and is always found combined with other elements such as oxygen, silicon, and fluorine. All structured data from the file and property namespaces is available under the creative commons cc0 license. This mild protocol can be used to simplify the synthesis of a speci. Carbenes and carbene complexes i massey university. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the r 2 co group into the related r 2 cch 2 derivative.
Nonwittig type reaction of tebbe reagent with acyl chloride. Download pdf while writing, i stare through lenses held in place by lightweight and. We found that the major product of the reaction of tebbe reagent with an acyl chloride was the corresponding methyl ketone 3 table i. Entries b, d, and g illustrate the important point that olefin positional integrity is maintained throughout the reaction. It is a red solid that is pyrophoric in the air, and thus is typically handled with airfree techniques. Comparison of the two reagents for a variety of ketones shows that the tebbe reagent gives better product yields than the wittig reagent.
Because they are less basic than the alkylidenenephosphorane wittig reagents, lombardo reagents. All structured data from the file and property namespaces is available under the. Tebbes reagent contains two tetrahedral metal centers linked by a pair of. Inspection of table i reveals that the reaction of the tebbe reagent 2 with a variety of substrates is a general, highyield synthetic operation which will tolerate both ketal and olefin functionality. Structural elucidation of the illustrious tebbe reagent article in organometallics 331. Tebbe olefination an overview sciencedirect topics. Tebbe s reagent is the organometallic compound and titanium and aluminum. The sterically crowded, monoanionic scorpionate ligand tptbu,me provides a unique environment for the isolation of discrete rareearth metal complexes with ych3. It exhibits carbenoid behavior after the addition of a catalytic amout of pyridine. Tebbes reagent 1 is an organometallic compound and. Spotlight 204 this feature focuses on a reagent chosen by a postgradu. Titanium reagents for the alkylidenation of carboxylic acid and carbonic acid derivatives richard c.
The titaniumbased tebbe reagent is a valuable tool when converting carbonyl groups into exoolefins. When 19 was treated with the tebbe reagent, the dimer 23 was produced, presumably through a cope reaction of the intermediately generated. The tebbe reaction was found to be more capricious, and it worked successfully only in small scale 50 mg of compound 16 and in the presence of a large excess of tebbe reagent from 4 to 8 equivalents, giving the target compound 18, but only in limited yield 37%. What does tri reagent do tri reagent solution also sold as trizol is a mixture of a mixture of guanidine thiocyanate and phenol in a monophase solution that is used for the isolation of dna, rna and protein from biological samples of human, animal, plant, yeast, bacteria, and virus. Wittig reagents olefination sigmaaldrich sigmaaldrich. Mechanism, references and reaction samples of the tebbe petasis olefination. Olefinations required at least two equivalents of tebbe s reagent. Cc bond formation 107 lowvalent ti cho cho jacs 1984, 106, 723 o ohc ome ome oh oh ome ome ticl 4, zn, pyridine 86 % tetrahedron lett. Editor inchief, european journal of soil biology thunen institute of biodiversity, braunschweig, germany send an email to christoph c tebbe. Structure finally resolved for the famous tebbe reagent.
The titaniumbased tebbe reagent is a valuable tool when converting carbonyl groups into exoolefins the reagent can be used for the methylenation of not only aldehydes and ketones, but also esters, lactones, amides, and thioesters, which cannot be achieved by the wittig reagent. Also, the petasis reagent, cp2tich32, is readily prepared from titanocene dichloride, as shown below. To send an email to christoph c tebbe please complete the short form below. Its disadvantages are its high sensitivity to both moisture and air, its lewis acidic character, and the fact that it is limited to methylenation. After the addition, the reaction mixture is allowed to warm to. Pdf download buy article permissions and reprints all articles of this category ketone methylenation has been accomplished using the tebbe and the wittig reagents.
Organometallics are useful reagent, catalyst, and precursor. C can generate a reactive titanocene methylidene species, which in situ converts a variety of carbonyl compounds, such as aldehydes, ketones, esters, and lactones, to the corresponding olefins. Olefinations required at least two equivalents of tebbe s reagent drives the reaction to completion. The following diagram shows two typical transformations of these alkylidene complexes. This page was last edited on 29 february 2016, at 11. Pdf attempts to prepare an allcarbon indigoid system. They can be synthesized from an alkyl halide and a triphenyl phosphine, followed by deprotonation with a strong base such as n. A rareearth metal variant of the tebbe reagent request pdf. Attempts to prepare the homologous titanium aluminum reagents, i. Christoph c tebbe editorinchief european journal of. The petasis reagent me 2 ticp 2, dimethyltitanocene undergoes similar olefination reactions with ketones and aldehydes. It is used in the methylenation of carbonyl compounds. Grubbs biographical i was born at home in rural kentucky in 1942, in a house that my father, howard, had built.
1456 630 1165 269 1267 403 714 182 32 462 1358 989 332 422 363 565 519 1121 1279 1275 793 141 656 482 1346 240 1119 480 1396 491 286 483 443 622 983 651 718 951 1381