Corey-Fuchs

Scientists at DuPont Merck Pharmaceuticals [31] had also developed a new process to prepare 37, based on a modification of the Corey-Fuchs method, from cyclopropylaldehyde, prepared by thermal rearrangement of butadiene monoxide. 

The dibromoalkene S-40 can be prepared from S-ethyl lactate by introduction of the MEM (methoxyethoxymethyl) protecting group, reduction to the O-protected lactaldehyde and Corey-Fuchs carbonyl olefination (Scheme 19). The l -enantiomer of 40 is available analogously from f -isobutyl lactate and serves as the reagent in the enantiomeric series. The lithium carbenoid S-41 is generated from S-40 by treatment with n-butyllithium in diethyl ether and reacted with aliphatic and aromatic aldehydes in tetrahydrofuran. High diastereoselectivities are reached, as shown in Scheme 19 . ... 

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

The olefination of cyclobutanones with the tetrabromomethane/triphenylphosphane reagent (Corey-Fuchs reaction) affords the dihaloalkene in the usual manner.241,242... 

See, for example, Rabinowitz Marcus J. Am. Chem. Soc. 1962, 84, 1312 Ramirez Desai McKelvie J. Am. Chem. Soc. 1962, 84, 1745 Corey Fuchs Tetrahedron Lett. 1972, 3769 Posner Loomis Sawaya Tetrahedron Lett. 1975, 1373 Suda Fukushima Tetrahedron Lett. 1981, 22, 759 Gavina Luis Ferrer Costero Marco J. Chem. Soc., Chem. Commun. 1985, 296 Li Alper7. Org. Chem. 1986, 51, 4354. 

The reaction sequence 11 13 is known as the Corey Fuchs pro- Solution... 

The one-step Seyferth procedure offers an alternative to the Corey -Fuchs sequence. After a Horner-Wadsworth-Emmons olefmation of an aldehyde 37 to an unsaturated diazo compound 38. elimination of nitrogen and [1,2]-rearrangement of the resulting vinylcarbene 39 leads here as well to a Cy-extended terminal alkyne 40.19... 

A modification of the Corey-Fuchs Reaction involves the reaction of the intermediate alkynyllithium with an electrophile prior to aqueous work-up, giving a chain extension product ... 

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. 

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. 

Step 1 Wittig olefmation gives the ( )-alkene as the major product (93 7). Step 5 Corey-Fuchs alkynylation. 

A two-step synthesis of arenediynes from arene-1,2-dialdehydes has been reported (Scheme 15). Dibromomethylenation of dialdehydes under Corey-Fuchs conditions provides the tetrabromides, which on treatment with n-BuLi or LDA afford 3,4-unsaturated 1,5-diynes, the key structural moiety present in several naturally occurring... 

Application of the Corey-Fuchs olefination to thioxanthone affords the 1,1-dibromoalkene 366 from which the 1,1-bis(trimethylsilylethynyl)alkene can be obtained by a double Sonogashira coupling reaction. Desilylation yields the 1,1-diethynylalkene (Scheme 86) <2004JA3108>. 

Sulfone 47 was prepared in nine steps from known iodide 69 by the sequence shown in Scheme 17.15. After initial conversion of 69 into aldehyde 70 by cyanide displacement and reduction with diisobutylaluminium hydride (DIBAL), a Corey-Fuchs alkynylation25 yielded alkyne 51, the key substrate needed for the proposed carboalumination-epoxide ring-opening step. Carboalumination26 was achieved by treating... 

Fig. 14.32. Aldehyde alkyne chain elongation via [l,2]-rearrangement of a vinyl carbenoid (Corey—Fuchs procedure). The aldehyde and phosphonium ylide A generated in situ undergo a Wittig olefina-tion and form the 1,1-dibro-moalkene (B). In the second stage, the dibromoalkene is reacted with two equivalents of n-BuLi and the vinyl carbenoid D is formed stereoselectively. The carbenoid undergoes H migration to form the alkyne C. The alkyne C reacts immediately with the second equivalent of n-BuLi to give the lithium acetylide and is reconstituted by reprotonation during aqueous workup.

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