Type-18 or -23 benzocycloheptadienones are readily prepared by ring-closing olefin metatheses. Adding Br to 23 and eliminating HBr gave the bromoolefin 28 using DBU or its isomer iso-28 using DABCO, both with near-perfect regiocontrol. Both 28 and iso-28 underwent Sonogashira, Suzuki, Negishi, and Heck couplings as well as Pd-catalyzed alkoxycarbonylations. Hydrolysis of the resulting α-ketoketals and enolization of the liberated α-diketones delivered a portfolio of hitherto unknown 3,4-benzotropolones. The 8-ethoxycarbonylated dimethyl-3,4-benzotropolone 50 obtained by this route was dimethylated to give goupiolone A (52). This synthesis encompasses 9 steps from 22, that is, half as many as the only previous synthesis (19 steps). A variant of our route afforded the 1,8-dibromide 54. Coupling with excess phenylboronic acid and ketal hydrolysis provided the diphenylated benzotropolone 56 and suggests a strategy, by which the natural bispulvinone aurantricholone (7) might be reached.
The naturally occurring γ-lactones (+)-methylenolactocin (13) and its enantiomer, (+)-protolichesterinic acid (14) and its enantiomer, (+)-rocellaric acid (15), and the methylene bis(γ-lactone) (-)-avenaciolide (16) were synthesized with 95-98 % ees in very few steps. Enantiocontrol was imposed by the asymmetric dihydroxylation of trans-configured β,γ-unsaturated carboxylic esters (namely compounds 1i, 1j, and 1n) with AD mix-α ® [for the levorotatory target structures, ex-
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.