O cross coupling

Commensurately with the development of various catalyst systems, the Pd-catalyzed G-O cross-coupling has found a number of synthetic applications. Examples include the syntheses of the protein kinase G (PKC) activator (+)-decursin,104 the natural product heliannuol E,105 a chiral 2-methyl chroman,106 and a series of aryloxy and alkoxy porphyrins.107 The Buchwald-Hartwig coupling has also been utilized in the preparation of a heterocycle library.108 Intramolecular O-arylation has also been achieved in the reactions of enolates with aryl halides leading to benzofur-ans.109,110 Finally, a double cross-coupling between an 0-dibromobenzene and a glycol has also been applied for the preparation of benzodioxanes (Equation (16)).1... 

Scheme 14.11 Copper-assisted nickel-catatysed C-O cross-coupling of vinyl halides wi phenols.

Bromobenzyl thiopropargyl ethers undergo a microwave-assisted cyc-locarbopalladation-palladium(O) cross-coupling cascade reaction with stan-nanes or boronic acids producing thiochromans with an exocyclic double... 

SCHEME 20.32 Influence of the phosphine ligands in the C—O cross-coupling. 

SCHEME 20.36 Cu-catalyzed C—O cross-coupling of aryl hahdes with phenols. 

The C—O cross-coupling of primary and secondary alcohols with aryl halides has been synthetically challenging due to p-hydride elimination (Schane 20.38, see Scheme 20.2). This has been overcome using binaphthyl-based phosphines L98 and L90 [112]. Buchwald and coworkers have explored sterically hindered phosphines for the alkoxylation of aryl substrates with secondary alcohols, and ligands L99-L100 with 1-phenyl and naphthyl backbone exhibited superior results (Scheme 20.39) [113]. 

The diaryl ether motif is abundant in a number of natural products and medicinally significant compounds. Evans and coworkers employed the C—O cross-coupling for the synthesis of tyrosine derivative 17 (Scheme 20.48) [58], which is an intermediate in Hems synthesis of... 

In 2008, Bolm s group [135] reported the Fe-catalyzed C-O cross-couplings of phenols with aryl iodides. The reactions were conducted using FeClj (10mol%), 2,2,6,6-tetramethyl-3,5-heptanedionato (TMHD) (20 mol%), and CSjCOj (2 equiv) in DMF at 135 °C for 20 h. The reaction scope and functional group compatibility were successfully demonstrated and the yields were generally very good. 

C-N and C-O Cross-coupling with Boronic Acid Derivatives 1225... 

Batey and Quach have investigated alkenyl and aryl trifluoroborate salts as coupling agents. Their earlier publication [47], disclosed a C-O cross-coupling protocol... 

A dimer 263 formed using nickel(O) cross-coupling was dibrominated at the only available positions, then dUithiated, and reacted with (PhS02)2S to obtain the tetramethyl-DTT 267 (Scheme 66) [100]. 

Likewise, a domino C-N/C-O cross-coupling process for the assembly of oxazoles was reported using 1,2-dihaloalkenes as the electrophilic partners [121]. When starting fi om dibromoaUcenes a strong preference for the formation of 2,5-disubstituted oxazoles was observed (ratios up to 11 1). The more reactive diiodoatkenes reacted unselectively at both positions (Scheme 35). 

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