Lignin natural products offer a multitude of structural variety. Despite their diverse complexity, the biosynthesis is proposed to feature a common oxidative coupling of two propenyl phenols, resulting in a bis--quinone methide, such as or . In this communication, Albertson and Lumb elegantly accessed such an intermediate through the opening of a cyclobutane. Indeed, bis--quinone methides and underwent 5--trig cyclizations to result in the lignin natural products tanegool and pinoresinol.
Ferulic acid was first converted into cyclobutane . For the synthesis of tanegool, reduction led to key intermediate . Then, radical-induced cyclobutane opening with iron trichloride gave the natural product in 59% yield together with 15% of its C7′ epimer. The same strategy was used to synthesize pinoresinol by first epimerizing the α-position of diester . After reduction and deprotection of , radical ring opening resulted in intermediate , which cyclized to pinoresinol as a single diastereomer in 48% yield.
Pinoresinol is synthesized by the ..