Metal-Catalyzed Methodologies

Through the years, the development of transition metal-catalyzed methodologies, notably involving cyclotrimerization and Sonogashira or Heck cross coupling, has paved the way for rapid and efficient access to aryl glycoclusters with desired and controlled valency. 

The VO(acac)2 based oxidative system was employed to epoxidize various double bonds under mild conditions. Thus, a one-pot synthesis of 2,3-dihydrobenzo[h]furanols was achieved in high regio- and diastereoselective manner in the presence of a catalytic amount of TFA (20 mol%). This metal-catalyzed methodology was shown to be more practical and superior to the previously employed m-CPBA based method <02SL942>. 

In 2012, Maes and co-workers reported a new transition-metal-catalyzed methodology for the direct C2-H functionalization of piperidines [67], via pyridine-directed Ru-catalyzed C(sp )-H alkylation with alkenes [68]. Based on previous work [69-73], they discovered that a combination of a bulky alcohol (2,4-dimethyl-3-pentanol) and a catalytic amount of a carboxylic acid [74] is necessary to avoid side reactions such as isomerization and/or reduction of the alkene reactant (Scheme 11). They successfully applied this method to the total synthesis of ( )-... 

Heteroaryl phosphonates are common motifs in biological compounds and have stimulated the development of transition metal-catalyzed methodologies for C-P bond formation [68]. Phosphonated thiophenes 43 are accessible via silver-catalyzed dehydrogenative cross-coupling of thiophene 1 with dialkyl phosphites 42 (Scheme 19) [69]. The reaction is performed in aqueous dichloromethane, proceeds regioselectively at the a-position, and utilizes silver(l) nitrate as catalyst and the oxidant potassium persulfate. 

C-H Functionalization. The last decade has seen the development of an increasing number of conditions to functionalize p5Tidine regioselectively via C-H activation. The various metal-catalyzed methodologies essentially provide access to C2 functionalized arylated, olefinated, or alkylated products, and the activation of pyridine via coordination to the nitrogen lone pair is commonly encountered. For instance, the one-pot amination/benzoylation procedure provides access to N-benzyoyliminopyridinium yUde in 96% yield (eq 29). ... 

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