Cobalt-Promoted Dimerization of Aminoquinoline Benzamides

A method for aminoquinoline-directed, cobalt-promoted dimerization of benzamides has been developed. Reactions proceed in ethanol solvent in the presence of Mn­(OAc)₂ cocatalyst and Na₂CO₃ base and use oxygen as a terminal oxidant. Bromo, iodo, nitro, ether, and ester moieties are compatible with the reaction conditions. Cross-coupling of electronically dissimilar aminoquinoline benzamides proceeds with modest yields and selectivities

Cobalt-Catalyzed Direct Carbonylation of Aminoquinoline Benzamides

A method for direct carbonylation of aminoquinoline benzamides has been developed. Reactions proceed at room temperature in trifluoroethanol solvent, use oxygen from air as an oxidant, and require Mn­(OAc)₃ as a cocatalyst. Benzoic and acrylic acid derivatives can be carbonylated by carbon monoxide affording imides in good yields. Halogen, nitro, ether, cyano, and ester functional groups are tolerated. The directing group can be removed under mild conditions affording phthalimides

Cobalt-Catalyzed, Aminoquinoline-Directed Coupling of sp² C–H Bonds with Alkenes

A method for cobalt-catalyzed, aminoquinoline-directed <i>ortho</i>-functionalization of sp² C–H bonds with alkenes has been developed. Reactions proceed at room temperature in trifluoroethanol solvent, use oxygen from air as an oxidant, and require Mn­(OAc)₃ as a cocatalyst. Benzoic, heteroaromatic, and acrylic acid aminoquinoline amides react with ethylene as well as mono- and disubstituted alkenes affording products in good yields. Excellent functional group tolerance is observed; halogen, nitro, ether, and unprotected alcohol functionalities are compatible with the reaction conditions

Tetrahydro-1,3-oxazepines via Intramolecular Amination of Cyclopropylmethyl Cation

An efficient synthesis of tetrahydro-1,3-oxazepines was developed involving the regioselective intramolecular amination of cyclopropylmethyl cation. The cation was generated by the abstraction of one imidate group in bis-imidate bearing a carbocation-stabilizing substituent. Using 1,1,2,3-tetrasubstituted cyclopropane substrates, highly diastereoselective intramolecular amination to <i>trans</i>-tetrahydro-1,3-oxazepines was achieved. The resulting tetrahydro-1,3-oxazepines were transformed to the homoallylamine derivatives in high yields

Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp² C–H Bonds

In this paper, we introduce arylphosphinic acid aminoquinoline amides as competent substrates for cobalt-catalyzed sp² C–H bond functionalization. Specifically, the feasibility of their coupling with alkynes, alkenes, and allyl pivalate has been demonstrated. Reactions are catalyzed by simple Co­(NO₃)₂ hydrate in ethanol or mixed dioxane/<i>t</i>BuOH solvent in the presence of Mn­(OAc)₃·2H₂O additive, sodium pivalate, or acetate base and use oxygen from the air as an oxidant. Directing group removal affords ortho-functionalized <i>P</i>,<i>P-</i>diarylphosphinic acids

Semisynthesis of Libiguin A and Its Analogues by Trans-Lactonization of Phragmalin

Libiguins are limonoids with highly potent sexual activity enhancing effects, originally isolated from the Madagascarian Meliaceae species Neobeguea mahafalensis, where they exist in only minute quantities. Their low natural abundance has hampered mapping of their biological effects. Here we describe an approach to the semisynthesis of libiguin A and its close analogues <b>1</b>–<b>3</b> starting from phragmalin, which is a limonoid present in high amounts in a commercially cultivated Meliaceae species, Chukrasia tabularis, allowing the preparation of libiguins in appreciable quantities