Aryl halides 1,3-dipolar additions

An alternative approach to multicomponent heterocycle synthesis involves the use of palladium catalysis to construct keto-alkynes for cycloaddition reactions. Muller has demonstrated the power of this approach in the construction of a range of aromatic heterocycles. For example, the palladium-catalyzed coupling of acid chlorides with terminal alkynes provides a method to assemble 36. The trapping of this substrate can provide routes to aromatic heterocycles. As an example, the addition of amidines provides a multicomponent synthesis of pyrimidines (Scheme 6.69) [97]. This same substrate 36 is available via the carhonylative coupling of aryl halides with terminal alkynes, providing a four-component synthesis of pyrimidines (98j. 36 can also be employed in 1,3-dipolar cydoaddition reactions. For example, cydoaddition... 

HMPA is also the only dipolar aprotic solvent to be used extensively with organomagnesium compounds. Large effects are observed when HMPA is used as either a solvent or a cosolvent. As examples, HMPA accelerates addition of an allylic organomagnesium compound to aryl-substituted alkenes, addition of (Trignard reagents to Carbon Monoxide, and addition of Propargylmag-nesium Bromide to allylic halides to give allene products. ... 

---