Oxygen terphenyl derivatives

A one-pot procedure for the synthesis of functionalized p-terphenyl derivatives has been reported that involves tandem aldol condensation/electrocyclization/oxidative dehydrogenation (Scheme 16.15) [18]. The intermediate electrocyclization product, namely, the dihydroaromatic derivative, is presumably oxidized by oxygen under basic conditions. 

Cinnamils (162) have surprisingly been found to evolve towards 2,3,8-triaryl vinyl fulvenes (163) and o-terphenyl derivatives (164) under NHC catalysis. The formation of these products has been rationalized via a mechanism involving a complex cascade process. Finally, a mechanistic investigation has been carried out on the NHC-catalysed aerobic oxidative esterification of aromatic aldehydes.Aryloin species have not only been identified as key intermediates of such oxidative reactions, but most importantly is that they have been shown to be the species which react with oxygen in the air and not the Breslow intermediates as previously suggested. 

Compounds will be discussed in Sections based on structural analogy, generally related to their biosynthetic ori n. Thus, simple / -terphenyls with a tricyclic C-18 basic skeleton, including their acyclic d-alkyl or O-acyl derivatives are treated in Section 2, normally in order of increasing number of oxygenated functions. Those showing a policyclic C-18 skeleton are discussed in Section 3, while Section 4 includes those possessing an alkylated skeleton (C-19 or more). The main biosynthetic pathways and selected synthetic methods are summarised in Sections 5 and 6, respectively. For the sake of completeness, terphenyls from lichens are shortly reported in Section 2.6. 

Degradation is determined by noting the disappearance of the characteristic peaks of the parent material in GC or MS analysis, and by the appearance of peaks indicating products the products are not always identified. Reaction pathways include direct dechlorination, and, in the presence of oxygen containing solvents, the formation of substituted hydroxy derivatives these are illustrated in Fig. 2. They may be accompanied by, or followed by, isomerisation and condensation, leading to the production of terphenyls, tetraphenyls, and dibenzofurans (Fig. 2). 

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