Recent advances in total synthesis of natural products by masked ortho-benzoquinones

The Diels-Alder adducts of masked ortho-benzoquinone (MOB) normally perform high regio- and stereoselectivity and are generated under mild conditions. The advantages of MOB include: (a) Containing highly functional moieties: alkene, diene, carbonyl, enone, and dienone; (b) Easily accessible from 2-methoxyphenol derivatives via oxidative dearomatization, and related 2-methoxyphenol easily prepared from commercially available starting materials; (c) The Diels-Alder adducts possessing unique features such as regio- and stereoselectivity and at least four contiguous stereogenic centers in one step. Furthermore, related bicyclo[2.2.2]octenone skeleton can be applied to further complex structure construction by various chemical transformations, such as radical cyclization, oxa-di-π-methane rearrangement, Beckwith-Dowd rearrangement, hydrogen atom transfer reaction, Cope rearrangement, Wanger-Meerwein rearrangement, carbonyl-ene reaction, aldol reaction, ring opening etc. Among these advantages, MOB system is prospected to continue as an important intermediate for total synthesis of natural products.