No abstract

A general method for the construction of diphenyl‐substituted carotenoids has been developed through the stereoselective synthesis of dienyl sulfones with a phenyl substituent. Systematic synthetic pathways to the dienyl sulfones were delineated starting from readily available acetophenones with para‐substituent X of various electronic natures, which provided the carotenoids with diverse physicochemical characteristics. The sulfone olefination method together with the Ramberg–Bäcklund reaction produced a 9,9′‐cis‐10,10′‐diphenylcarotene and all‐trans‐9,9′‐diphenylcarotenes. Conductance measurements of the all‐trans carotenoids by the scanning tunnelling microscopy break‐junction method revealed a positional effect of the phenyl groups as well as a polar effect of the phenyl substituent X according to the electronic nature.

A practical synthesis of coenzyme Q 10 has been developed. The route features an improved Friedel-Crafts allylation of tetramethoxytoluene with a para-chlorobenzenesulfonylsubstituted C 5 allylic chloride at 40°C. Replacement of the methyl ether protecting groups of the para-hydroquinone by [a]

New C5 sulfone building blocks containing a masked polar end group have been devised for the efficient synthesis of carotenoids with polar termini. Chemoselectivity or the regiochemical issue of the highly functionalized units has been carefully addressed depending on the soft or hard nature of electrophiles. These building blocks have been successfully applied to the syntheses of crocetin derivatives, crocetin dial and the novel crocetin dinitrile.