Enol triflates alkenes

Ketones can also be reduced to alkenes via enol triflates. The use of Pd(OAc)2 and triphenylphosphine as the catalyst and tertiary amines as the hydrogen donors is effective.226... 

Alkenyl trifluoromethanesulphonates (enol triflates) undergo Heck coupling with alkenes efficiently (equation 123)209a 215. This reaction is a useful variation of the use of vinyl halides not only because they are easy to prepare from the corresponding carbonyl compounds, but also because yields are good, and the stereochemistry of the triflate is largely maintained. 

Coupling with enol esters (7, 93). A new synthesis of an alkyl-substituted alkene involves coupling of a lithium dialkyl cuprate with an enol triflate,1 available from a ketone by reaction with triflic anhydride and 2,6-di-t-butylpyridine.2 A wide variety of organocuprates can be used and the geometry of the enolate is largely retained. Reported yields are in the range 60 100%. 

Although the coupling of aiyl halides with alkenes (commonly referred to as the Heck reaction) was first reported more than 25 years ago [ 1 ], only in the past decade has its enormous synthetic potential been realized [2], Within that time, the reaction has been extended to many substrates, including vinyl iodides and bromides and enol triflates. Moreover, the intramolecular variant has become one of the more important reactions for the formation of carbon-carbon bonds and has emerged as a premier method for the construction of quaternary carbon centers. The ability of intramolecular Heck reactions to reliably fashion carbon-carbon bonds in polyfunctional molecules has led to wide application of this reaction at the strategy level for the synthesis of complex natural products [2g],... 

The conversion of carbonyl compounds to their enol triflates provides a very simple way to couple the carbonyl carbon to an alkene. In general, however, aryl... 

Ketones and aldehydes are converted to alkenes by the hydrogenolysis of their enol triflates with formate. The steroidal enone 524 is converted to the dienol triflate 525 and then to the 1,3-diene 526 by the hydrogenolysis with tributylammonium formate... 

Ethyl diazoacetate (228 mg, 2.0 mmol) was added at a controlled rate over a 6-8 h period to a stirred mixture of the alkene (20.0 mmol) or diene (10.0 mmol) and the catalyst (0.01 -0,02 mmol) under and ordinarily at 25 C. For copper(I) triflate catalyzed reactions with enol ethers, the diazo ester dissolved in the enol ether w as added to copper(II) triflate in EtjO in order to minimize polymerization of the enol ether. Alkenes were generally purified by distillation prior to their use. The initial solubility of the transition metal compound was dependent on the alkene employed, and, with the exception of Rhg(CO)jg, bis(acetylacetonato)copper(II), and copper bronze, homogeneous solutions were obtained prior to or immediately after the initial addition of ethyl diazoacetate. 1 h after addition was complete, EtjO was added, the resulting solution was washed twice with sat. aq NaHC03 dried (MgSOJ. EtjO and excess alkene were distilled under reduced pressure. The desired cyclopropanes were obtained either by fractional bulb-to-bulb distillation or by preparative GC (Table 8). 

The coupling of enol triflates with y-hydroxycrotonic esters gives butenolides. The method is suitable for cardenolide synthesis. Nonactivated alkenes also undergo coupling. ... 

For strychnine 3, the ketone 11 was converted to the alkene 12 by reduction of the enol triflate derived from the more stable enolate. Deprotection and acylation gave 13, which was cyclized with Pd to give, after equilibration, the diene 14. Alkylation, to give 15, followed by Pd-mediated cyclization then gave 16, which was reduced and cyclized to (-)-strychnine 3. 

Phase-tranter Conditions. The Heck conditions described above are not useful, however, for a large number of alkenic substrates. A sometimes serious drawback is the high temperature (ca. 100 °C) often required. Upon addition of tetrabutylammonium chloride ( phase-transfer conditions or Jeffery conditions ), aromatic halides or enol triflates react under mild conditions with vinylic substrates or allylic alcohols. Variations of these conditions include the optional or additional presence of silver or thallium salts. The effect of using different salts, bases, catalysts, solvents, and protecting groups in the coupling of aminoacrylates with iodobenzene has been studied. ... 

Deoxygenation of Carbonyls. Carbonyl compounds can be deoxygenated to form alkenes in a palladium-catalyzed reduction of enol triflates (eq 72). The reaction is quite general, and has been applied to aryl as well as alkyl enol triflates. ... 

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