## 2 Sequences Based upon Alkynylation and Carbopalladative Insertions  
Generally speaking, the majority of Pd-catalyzed sequential, consecutive, and domino processes involve an insertion of the palladium species into a carbon-carbon bond [41; 42; 43]. Carbopalladation of alkynes is particularly fascinating because, on the one hand, triple bonds are excellent ligands for transition metals, and on the other hand the complexes do not exit the catalytic cycle by \(\beta\)-hydride eliminations as known for Heck vinylations. For these complexes, possible exits are Pd-mediatednucleophilic trapping or a subsequent transmetallation, respectively. To date, the known catalytic systems for Sonogashira reactions are those with the highest capability of subsequent Pd- or Pd-Cu-cocatalyzed cyclizations. Thus, selected developments in Pd-catalyzed cascade cyclizations are discussed in the following. Based on _ortho_-iodo phenol or an _ortho_-iodo benzylalcohol as an aryl halide and phenylacetylene as an alkynyl coupling partner, a Pd-catalyzed domino sequence has been reported where cycloisomerization subsequent to the coupling step affords benzofuran **1** or benzoisofuran **2**, respectively [44]. Three different NHC-Pd-pyridine complexes **3-5**, where NHC is 1,2,4-trimethyltriazolezolydiylidene (**3**), 1,3-dimethylimidazolzolylidene (**4**), and 1,4-dimethyltriazolezolyidene (**5**), respectively, have been successfully employed (Scheme 1). **Scheme 1. ** Sequentially Pd-catalyzed alkynylation-hydroxaryloxylation synthesis of benzofuran **1** and isobenzofuran **2**. Accordingly, the group of [PERSON] and coworkers reported a three-component coupling-cyclization sequence affording benzofuran **6** or indole **7** involving an initial amine propagylation via classic substitution and a subsequent Sonogashira coupling-cyclization using the established Sonogashira conditions (Scheme 2) [45]. **Scheme 2. ** Consecutive amine propagylation-Sonogashira coupling-cyclization synthesis of benzofuran **6** and indole **7**. Another application of Sonogashira conditions in coupling and subsequent cyclization has been published by [PERSON] and coworkers [46]. Despite mechanistic incomprehensibilities pertaining to a formal oxidation step, the cooperation of palladium and copper as catalysts provides thiophene anellated \(\alpha\)-pyrones **8** and **9** (Scheme 3, Table 1). **Scheme 3. ** Sequentially Pd-catalyzed alkynylation-cyclization-alkynylation synthesis of 4-alkylvinylthieno[2,3-c]pyran-7-ones **8** and 7-alkylnylthieno[3,2-c]pyran-4-ones **9**. Another remarkable extension of the Sonogashira catalyst system has been published by [PERSON], [PERSON], and [PERSON] in which they employed the catalytic system in a Sonogashira alkynylation-carbopalladation-C-H activation-cyclization sequence [47]. Their three-component synthesis afforded an access to 3-(diaryl-methylene)oxidoles **10** using the initial catalyst source for various steps (Scheme 4, Table 2). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Entry** & **Thiophene** & **Alkyne** & **Alkynylthienopyran-7-Ones 8 and 9 (Yield)** \\ \hline
1 & & & \\
2 & & & \\
3 & & & \\
4 & & & \\
5 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selected 4-alkylnylthieno[2,3-c]pyran-7-ones **8** and 7-alkylnylthieno[3,2-c]pyran-4-ones **9** via sequentially Pd-catalyzed alknylation-cyclization-alknylation sequence. The use of _ortho_-iodo anilines provides access to a variety of substrates for consecutive domino reactions which can then be applied to the synthesis of heterocycles [5; 6; 7; 9; 48; 49; 50; 51] and functional materials [39]. One example is the preparation of (tetrahydroiosobenzofuran) spiro-benzofuranones or spiro-indolones in moderate to excellent yields by use of the domino insertion-coupling-isomerization-intramolecular Diels-Alder sequence of alkynoyl _ortho_-iodo phenolesters or alkynoyl _ortho_-iodo anilides and propargyl allyl ethers [52; 53]. The particular interest in the target compounds is based on their solution and solid state luminescence.