Aldehydes Corey-Fuchs reaction

A general one-pot procedure for the synthesis of alkynes from aldehydes (Corey-Fuchs reaction) that involves the synthesis of the triphenylphosphonium dibromomethane reagent has been explored by Michel and coworkers. In general, the base of choice is f-BuOK, but in case of the N-Boc piperidine, use of BuLi in order to avoid unwanted side reactions between the carbamate and the acetylide function provides a cleaner reaction at low temperature (eq 64). 

Terminal alkenylstannanes can be prepared after homologation of aldehydes via the Corey-Fuchs reaction.95... 

Another common method for the conversion of an aldehyde into an alkyne is the transformation of the aldehyde via a Corey-Fuchs reaction into a geminal vinyl dibromide followed by reaction with nbutyllithium and aqueous work-up.22... 

Steps 1-2 Corey-Fuchs reaction aldehyde to terminal alkyne transformation. 

Steps 1-2 Conversion of a ketone to a terminal alkyne (compare with Corey-Fuchs reaction where an aldehyde is converted to a terminal alkyne). Step 4 Me2CuLi adds to the acetylenic ester in a conjugate manner to provide (Z)-olefin. 

W.J. Kerr and co-workers carried out the total synthesis of (+)-taylorione starting from readily available (+)-2-carene and using a modified Pauson-Khand annulation with ethylene gas as the key step. The key terminal alkyne intermediate was prepared by the Corey-Fuchs reaction. Interestingly, the ketal protecting group was sensitive to the excess of CBr4, so the addition of this reagent had to be monitored carefully to cleanly transform the aldehyde to the desired dibromoolefin. 

A bonanza of Heck reactions was used by Tietze25 in the synthesis of cephalostatin analogues. Corey-Fuchs reaction on the aldehyde 167 gives the alkene 168 from which the trans Br atom is stereoselectively removed by Pd-catalysed tin hydride reduction to give the Z-vinyl bromide 169. This reaction is discussed below under Stille coupling. 

Sol 3. (d) The first step involves Corey—Fuchs reaction One-carbon homologation of an aldehyde to dibromoolefin, which is then treated with n-BuLi to produce a terminal alkyne. 

Corey-Fuchs reaction is a two step reaction converting an aldehyde to an alkyne by one-carbon homologation of the aldehyde. The Wittig-like reaction of aldehyde 1 and dibromocarbene forms dibromoalkene 2. The treatment of dibromoalkene 2 with two equivalent of -BuLi form a lithium alkynylide, quenched by eletrophiles, such as proton, CO2, aldehydes, ketones, and alkyl halides to form alkyne 3. 

Alkyne 13 was prepared from aldehyde 9 by Corey-Fuchs reaction (10), alkylation (11), 1,2-Wittig rearrangement (12) and silylation reaction. The reaction of alkyne 13 and BuaSnH afforded compound 14 via a 5-exo-dig cyclization and the cleavage of Si-0 bond by MeLi. ... 

The enantiomerically pure alkynylogous amino acids 24 were prepared from aldehyde 23 by Corey-Fuchs reaction. ... 

The reaction sequence in steps two and three is known as the Corey-Fuchs method to create an alkyne from an aldehyde 10 Reaction of triphenylphosphane with carbontetrabromide gives phenylphosphane-dibromomethylene. This reagent then transforms aldehyde 19 into the corresponding dibromoalkene 20 thereby extending the chain by one carbon. Reaction of the bromo compound with two equivalents of n-butyllithium in THF at -78 °C results in the rapid formation of the acetylenic lithio derivative which forms the terminal acetylene 21 upon aqueous work-up. 

Fig. 11. 29. Aldehyde — alkyne chain elongation via [1 -rearrangement of a vinyl carbenoid (Corey-Fuchs procedure). The aldehyde and phosphonium ylide A generated in situ undergo a Wittig reaction and form the 1,1-dibromoalkene. In the second stage, the dibromoalkene is reacted with two equivalents of n-BuLi and the vinyl carbenoid C is formed. The carbenoid undergoes H migration to form the alkyne B. The alkyne B reacts immediately with the second equivalent of w-BuLi to give the lithium acetylide.

French chemists have been able to increase the yields to 85-90% by use of a 40 60 mixture of THF—ether as solvent instead of pure THF. Note that Corey and Fuchs (4, 550) have prepared 1,1-dibromo-l-alkenes by the reaction of an aldehyde with triphenylphosphine, carbon tetrabromide, and zinc in methylene chloride. 

This transformation was first disclosed by Corey and Fuchs in 1972. Three aldehydes, an aromatic, a linear aliphatic and a cyclic aliphatic aldehyde were chosen to show the generality of this reaction. For all three aldehydes, the reaction proceeded well. 

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