Cross-coupling, palladium-catalyzed, benzene

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

The bromine atoms in 2,5-dibromo-l,3,4-thiadiazole 54 undergo a palladium-catalyzed Stille reaction with the organostannyl derivative 55 (Equation 7) <1998CEJ2211>. The thiadiazole 54 was co-polymerized with diethynyl benzene 56 (Equation 8) and diethynyl pyrrole in a Sonogashira cross-coupling reaction <2005MM4687>. 

The benzene derivatives containing the fluorinated sulfone have been prepared either by nucleophilic substitution of the 4-fluorophenyl derivative (e.g. 1) or by starting with the appropriately substituted sodium thiophenoxide and reacting with perfluoroalkyl iodide follow by oxidation with either MCPBA or chromium oxide (12. li.) The biphenyl derivatives have been prepared by palladium catalyzed cross coupling chemistry of the 4-bromophenyl derivative (e.g. 2) with substituted phenyl boronic acid (yields 37-84%) (JLH, .). Compound 16 has been prepared by palladium catalyzed cross coupling of (4-bromophenyl)perfluorohexyl sulfone with vinyl anisole in 37 % yield (JJL). The vinyl sulfones, 7 and 9, have been prepared by condensation of CH3S02Rf (JJL) with the appropriate aldehyde (yields 70,and 73%) following a literature procedure (1 ). Yields were not optimized. 

Suzuki couphng, the palladium-catalyzed cross-coupling of aryl or vinyl hahdes with organoboronates, is employed widely in organic synthesis. The reaction is most often carried out in an organic solvent (benzene) in the presence of a base [228]. Because of the reasonable stabihty of boronic acids and esters towards hydrolysis, Suzuki couphng can also be carried out in aqueous media. An extensive study of the reaction has shown that similar results are obtained in aqueous and non-aqueous systems [229]. 

Salt-activated Al(TMP)3-3LiCl can be used to achieve the functionalization of substituted benzenes and naphthalenes. Provided that a reduced temperature is used, the reaction tolerates the presence of functional groups (Table 27.7) [20]. Al(N(CH(/-Pr)r-Bu)r-Bu)j-3LiCl is an efficient alternative, for example, to achieve subsequent palladium-catalyzed cross-coupling [102]. 

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