Heck/Sonogashira tandem reaction

Sonogashira/nucleophilic addition (Scheme 7.34) [70], The reaction started by the Ugi-4CR, giving the intermediate 82, which was transformed into the enyne 83 by a Heck-Sonogashira tandem reaction. Finally, the activated enyne evolved an aza-Michael-type addition to give the final six-component product 84. 

NHC-Pd(ll) complexes have also been used in tandem reactions involving a Sonogashira couphng and hydroalkoxylation of the resulting alkyne for the synthesis of benzofurans [131] as well as sequential Heck-Sonogashira couphngs [132] (Scheme 6.44). 

Scheme 6.44 Tandem Sonogashira-hydroaUcoxylation and Sonogashira-Heck reactions...

Since aikenes and aikynes can be prepared via Heck and Sonogashira reactions, respectively, tandem processes are also possible for lactone synthesis [71-77]. Appropriately, o-iodobenzoic acids can generate both phthalide and isocoumarin derivatives under Pd catalysis, with a Cul co-catalyst favoring the former and... 

Also exploiting an intramolecular C—S bond formation, Bryan et al. extended their investigation of gem-dihalovinylarene substrates in the synthesis of heterocycles to encompass a thiol analogue (Scheme 34.38, disconnection D-2). The combination of an unusual palladium-catalyzed S-alkenylation with a second cross-coupling process, such as a Suzuki, Heck, or Sonogashira reaction led to diversely functionalized benzothiophenes such as 67, produced in excellent yield (Scheme 24.40) [132], Routes incorporating a tandem carbonylation step [133] and a direct arylation [117] process have subsequently been reported. 

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