Transition Metal-Catalyzed Intramolecular Amination and Hydroamination Reactions of Allenes

Medium and Large N-Heterocycle Formation via Allene Hydroamination with a Bimetallic Rh(II) Catalyst

We report the synthesis of a 2-phosphinoimidazole-derived bimetallic Rh(II) complex that enables intramolecular allene hydroamination to form 7- to 10-member rings in high yield. Monometallic Rh complexes, in contrast, fail to achieve any product formation. We demonstrate a broad substrate scope for formation of various N-heterocycles. Macrocyclizations that form 11- to 15-member N-heterocycles are also demonstrated. Mechanistic studies suggest that the reaction proceeds via reversible allene insertion with a Rh-hydride followed by C-N bond-forming reductive elimination. We hypothesize that the reactivity observed with our catalyst vs monometallic Rh complexes is derived from the bimetallic nature of our complex.

Palladium-Catalyzed Synthesis of 1-Vinyltetrahydro-β-carbolines and Aza-spiroindolenines: Access to the Syntheses of 1-Vinyl-β-carbolines and Eudistomins Y1 and Y2

A general synthesis of 1-vinyltetrahydro-β-carbolines (THBCs) has been achieved via palladium(0)-catalyzed cyclocondensation between allenyltryptamines and aryl iodides. Aza-spiroindolenines could also be accessed from the N-unsubstituted indole substrates by simply tweaking the reaction conditions. DDQ-mediated oxidation of THBCs easily afforded β-carbolines, which could be synthetically transformed into 1-aroyl-β-carbolines of pharmacological interest. Formal total syntheses of eudistomins Y1 and Y2 have also been achieved.

Catalytic intramolecular hydroamination of aminoallenes using titanium and tantalum complexes of sterically encumbered chiral sulfonamides

Titanium and tantalum catalysts supported by readily prepared chiral sulfonamide ligands catalyze hydroamination of aminoallenes that lack N-protecting groups.

Design and Synthesis of Flavonoidal Ethers and Their Anti-Cancer Activity In Vitro

Flavonoids are well-characterized polyphenolic compounds with pharmacological and therapeutic activities. However, most flavonoids have not been developed into clinical drugs, due to poor bioavailability. Herein, we report a strategy to increase the drugability of flavonoids by constructing C(sp²)-O bonds and stereo- as well as regioselective alkenylation of hydroxyl groups of flavonoids with ethyl-2,3-butadienoate allenes. Twenty-three modified flavonoid derivatives were designed, synthesized, and evaluated for their anti-cancer activities. The results showed that compounds 4b, 4c, 4e, 5e, and 6b exhibited better in vitro inhibitory activity against several cancer cell lines than their precursors. Preliminary structure–activity relationship studies indicated that, in most of the cancer cell lines evaluated, the substitution on position 7 was essential for increasing cytotoxicity. The results of this study might facilitate the preparation or late-stage modification of complex flavonoids as anti-cancer drug candidates.