## 2 Applications in Chemistry
### Metal-Catalyzed Miscellaneous Reactions
In order to obtain CF\({}_{3}\)-substituted tetrahydrobenzoxazonines **32**, [PERSON] and co-workers [85] reacted VECs **6** and trifluoromethyl benzoxazinone **33** in refluxing dichloroethane in the presence of tetrakis(triphenylphosphine)-palladium(0). Using this catalytic system, various nine-membered heterocyclic compounds **32** were isolated with 33-91% yields. In 2016, the catalytic and stereoselective formation of (\(Z\))-1,4-but-2-enediols **9** was reported through decarboxylative hydration of VECs **6** in the presence of water as a nucleophile [86]. The reaction was performed in DMF/H\({}_{2}\)O at room temperature, using a catalytic Pd precursor, Pd/bis(sulfoxide) and a bidentate phosphine ligand. The expected unsaturated 1,4-diols **9** were obtained with 50-98% yields with >99:1 \(Z\)-stereoselectivity (Scheme 22). While different groups such as aryl, naphthyl, and heteroxyl were efficiently incorporated into diols **9**, it is important to highlight that some specific substitutions, e.g., \(o\)-haloaryl or 3-pyridyl, required forced conditions with higher temperatures and larger amounts of Pd-catalyst (5 mol%) and phosphine ligand (10 mol%) in order to reach preparative yields. In order to illustrate the good reactivity of the (\(Z\))-1,4-but-2-enediols **8**, some chemical modifications were made, such as \(m\)-CPBA oxidation to the epoxide **2b**, high-yield conversion into the cyclic orthoester **34**, and copper-catalyzed chemoselective oxidocyclization to the isomeric lactones **35a** and **35b** (Scheme 23). **Scheme 21. ** Synthesis of nine-membered cyclic compounds **30**, starting from azadienes **31** and VECs **6**. **Scheme 22. ** Decarboxylase hydration of VECs **6**. Racemic VECs **6** were used for the stereoselective \(O\)- or C-allylation of phenols and \(N\)-allylation of 2-hydroxypyridines by use of 1-5 mol% of [Rh(cod)Cl]2 and 2-10 mol% of a chiral diphosphine as the ligand [(\(R\),\(R\))-QuinoxP*; (\(S\),\(S\))-DIOP or (\(R\),\(R\))-TBDM-SLIOP] [87]. Performed in dichloroethane or toluene over 24-48 h at temperatures ranging from r.t. to 80 \({}^{\circ}\)C, the reaction allowed exploration of an ample range of substrates, with yields exceeding 70% in most cases (see Figure 3 for selected examples). In this extensive study, carbonate **1e** was converted into compound **39a** (94% yield; 97% _ee_) by asymmetric \(O\)-allylation of 4-bromophenol **7b** (Scheme 24). [PERSON] and co-workers [88] described the alkaline earth metal-catalyzed reduction of cyclic and linear organic carbonates using a readily available magnesium catalyst (Scheme 25). These mild reaction conditions provided an indirect route for the conversion of CO2 into valuable alcohols. By using a low catalyst loading and avoiding ligands, a broad scope of compounds **40** was prepared via the selective corroboration with HBPin **41**, all with excellent yields. Specifically, cyclic carbonates **1** bearing substituents such as phenyl, methyl, hexyl, \({}^{1}\)Bu, as well as glycerol derivatives, were efficiently reduced with excellent yields, ranging from 88% to 95% within 3 h.  
Figure 3: Products of \(O\)-, C- and \(N\)-allylation **36a**, **37a** and **38a**, respectively. With a view to promoting C-H olefination of arenes and heteroarenes **42** by rhodium catalysis, [PERSON], [PERSON], and co-workers [89] explored the use of dichlor(pentamethylcyclopentadienyl)rhodium(III) dimer [(CP*RChCl2]2] as a catalyst with copper(II) acetate as the oxidant and additional silver hexafluoroantimonate. By using VEC **1e**, a series of \(o\)-olefinated benzamides such as **43** (Scheme 26) were obtained (49-94% yields). The authors also developed olefination of arylpyridines and indoles with 30-91% yield using unactivated aliphatic olefins under the same conditions, albeit using pivalic acid as a promoter.