Bruceolline D: 3,3-dimethyl-1H,4H-cyclopenta[b]indol-2(3H)-one

Abstract

Key indicators: single-crystal X-ray study; T = 173 K; mean (C-C) = 0.005 Å; R factor = 0.068; wR factor = 0.174; data-to-parameter ratio = 13.9.The title compound, C 13 H 13 NO, crystallizes with four independent molecules in the asymmetric unit. The 12-membered penta [b]indole rings are essentially planar, with maximum deviations ranging from 0.034 (4) to 0.036 (4) Å in the four unique molecules. In the crystal, weak C-HÁ Á ÁO interactions are observed, which link the molecules into chains along [010].

A Short, Protecting Group-Free Total Synthesis of Bruceollines D, E, and J

“…To our delight, the cyclization of o -chloroaniline with dione 12 proceeded smoothly to provide bruceolline D ( 5 ) in 88% yield (Scheme ). The structure was confirmed by X-ray crystallography …”

“…11 Protection of 14 at this stage would intercept the route used in the only previous synthesis of bruceolline E (6). 3 With bruceolline E ( 6) in hand, we turned our focus to the selective monoreduction of the dione moiety to furnish racemic bruceolline J (9). As expected, the ketone was reduced rapidly and selectively in the presence of the vinylogous amide with none of the possible bis-reduction product detected (Scheme 3).…”

“…The structure was confirmed by X-ray crystallography. 9 Oxidation of bruceolline D (5) to bruceolline E (6) proved straightforward by treatment of 5 with DDQ in aqueous acetonitrile (Scheme 2). 10 An alternative synthesis of bruceolline E (6) was investigated which involved Fischer or palladium-catalyzed cyclization to indole 13 and subsequent DDQ oxidation to indolone 14.…”