Arylboronic acids catalysis

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

Extensive use of Pd-catalyzed reactions was included in the synthesis of 2,6,8-trisubstituted purines (Fig. II).33 The synthesis started by anchoring dichloropurine to Rink resin via N9 linkage. Polymer-bound 2,6-dichloropurine (63) was selectively substituted at C6 via acid-catalyzed SNAr substitutions. In the absence of Pd catalysis, the substitution on C2 could be performed only with strongly nucleophilic amines. To expand the scope of C2 substitution, catalytic amounts of Pd were used. Under these reaction conditions arylboronic acids and amines successfully substituted the chloro atom on C2 to afford C2-C and C2-N bonds. Subsequently, the C8 position was brominated with a bromine-lutidine complex33 (66) to give resin 67. 

One of the most important contributions in metal enolate catalysis is the conjugate addition of arylboronic acids (115) to vinyl ketone derivatives (116) to give the corresponding aryl ketones (117) (equation number of advances have recently... 

Homogeneous, aqueous tv o-phase catalysis is also of industrial interest for the production of the important intermediate phenylacetic acid (PAA), -which is used in perfume and pesticides syntheses. The previous process (benzyl chloride to benzyl cyanide -with hydrolysis of the latter) suffered from the formation of large amounts of salt (1400 kg per kg of PAA). The new carbonylation method reduces the amount of salt by 60% and makes use of the great cost difference between —CN and —CO [79-81]. Finally, the Suzuki coupling of aryl halides and arylboronic acids, substituting Pd/TPPMS with Pd/TPPTS catalysts, should be also mentioned. 

Substitution reactions. Benzylation of phenols by benzyl methyl carbonates with Pd catalysis proceeds via transesterification and decarbonylation. Triarylmethanes are obtained from a reaction of benzhydryl carbonates with arylboronic acids. ... 

Arylations. Copper(II) acetate catalyzes the reaction of arylboronic acids with thiols and of amines with hypervalent arylsiloxanes. 4-Substituted imidazoles react with aryllead(IV) reagents (in dichloromethane at room temperature) to afford N-1 arylatcd derivatives regioselectively under catalysis of Cu(OAc)2. ... 

Another method for direct amination of aryl rings relies on arylboronic acids rather than on aryl halides, using ammonia (25% NH3 in water) and CuaO-catalysis. These are run in MeOH at ambient temperatures in the absence of a ligand, a base, or other additives. Air is crucial for catalysis increasing the temperature to even 40 °C lowered the yield as a result of a decrease in solubility of NH3. Yields of derived anilines are uniformly high, most between 80% and 93%. 

The rhodium-catalyzed addition of arylboronic acids to a, 3-unsaturated ketones was first reported by Miyaura in 1997 [44], and only a short time thereafter the first enantioselective addition was documented by Hayashi [45]. Excellent reviews are available that summarize the early developments in this rapidly expanding field of asymmetric catalysis [46] consequently, only recent advances wiU be included in this section. 

Both, Hayashi and Carreira developed, independently, chiral dienes as novel ligands in asymmetric catalysis (Figure 8.6) [66]. Early investigations by Miyaura revealed that the rhodium-catalyzed conjugate addition of arylboronic acids to a,P-unsaturated ketones could be very efficiently catalyzed by a rhodium(I) complex of cyclooctadiene [67]. As a consequence, the development of chiral cod-analogues... 

Axially chiral N-arylsuccinimides were prepared by the addition of arylboronic acids to l-(2-tert-butylphenyl)maleimide (103) (Scheme 8.25), and excellent diastereo- and enantioselectivities were obtained upon catalysis with the rhodium complex of diene 51 [90]. 

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