Palladium-catalyzed synthesis five-member ring

Compared with the synthesis of five-membered rings relatively little has been done on the synthesis of 8-lactones. Homoallylic alcohols can be converted into 8-lactones by rhodium-catalyzed hydroformyla-tion followed by oxidation (equation 48). The thallation and subsequent palladium-catalyzed carbonylation described earlier can also be used for the synthesis of six-membered rings (equation 49). ... 

While most of the carbonylative cyclizations focused on the formation of five-and six-membered rings, there are also a few examples known for the preparation of larger rings. For example, in 1999 the palladium-catalyzed synthesis of a 2,3,4,5-tetrahydro-l//-2,4-benzodiazepine-l,3-dione derivative was reported by BoceUi et al. [280]. Using 1-butyl-l(o-iodobenzyl)-3-phenylurea as a starting material at 80 °C under CO pressure, 91 % of the desired product was isolated (Scheme 2.42). 

C.i. Palladium-Catalyzed Allylation in the Synthesis of Five-Membered Ring Natural Product... 

The biological activity displayed by the perhydroazulenes, ranging from diuretic and anti-inflammatory to antitumor, combined with the unique bicyclo [6-3-0] system make them very attractive synthetic targets. The approach of Trost and Higushi to this class of compounds, exemplified by the total synthesis of isoclavu-kerin 65 (Scheme 12.12) [34], has the distinctive feature that it allows the simultaneous formation of both the five- and seven-membered rings through a palladium-catalyzed formal [3+2] cyclization as its key step [35]. 

Sultones are the internal esters of hydroxy sulfonic acids and are the sulfur analogs of lactones. Sultones are demanded scaffolds in medicinal chemistry research. Biological studies on sultones are mainly concerned with their toxicological, skin sensitization, and antiviral activities [20]. Sultones are synthetically useful heterocycles which can react with a variety of compounds to introduce the alkylsulfonic acid function and therefore used as sulfoalkylating agents [21]. There have been several new developments for the synthesis of sultones which have also been applied in the total synthesis of natural products. In recent years, the palladium-catalyzed direct arylation of several aromatics via a C-H bond activation using aryl halides has led to successes. An intramolecular version of this reaction has allowed the synthesis of several biaryls via the formation of five- to seven-membered rings. Thus, the sultones should be synthesized by C-H activation via two pathways (Scheme 4.14). 

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