Corey-Fuchs olefination

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>. 

Corey-Fuchs Dibromoolefination, Corey-Fuchs Homologation, Corey-Fuchs Olefination)... 

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 . ... 

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

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. 

With a bountiful supply of 69 at our disposal, the synthesis was continued by PCC oxidation to the aldehyde level and application of the Corey-Fuchs procedure [35] for chain homologation via dibromo olefin 70 to the acetylenic ester 71. Since amide bond construction next had to be implemented, this ester was saponified under mild conditions and the resulting carboxylic acid was activated by formation of a mixed anhydride with mesitylenesulfonyl chloride in advance of in situ condensation with 59. In order to preclude hydrolysis of the silyl ether functionality in 72, deacetalization had to be performed under anhydrous conditions in dry acetone containing a catalytic quantity of p-toluene-... 

Corey-Fuchs alkyne synthesis can be seen as a cousin of the Wittig olefin synthesis. 

Synthesis of bengamide E (3) from the D-threose derivative 37 has been reported (Scheme Corey and Fuchs dibromoolefination of 37 produced the olefin 38, which was treated with butyllithium to give the acetylene derivative 39. The acetylide anion of 39 was generated... 

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