Allyl‐Palladium‐Catalyzed Ketone Dehydrogenation Enables Telescoping with Enone α,β‐Vicinal Difunctionalization

A Tandem Dehydrogenation-Driven Cross-Coupling between Cyclohexanones and Primary Amines for Construction of Benzoxazoles

Herein, we report a transition metal-free, operationally simple, general method for straightforward syntheses of 2-substituted benzoxazoles from readily available cyclohexanones and aliphatic primary amines by an imine α-oxygenation-initiated cascade reaction sequence. The key to achieving high selectivity and excellent functional-group tolerance is the use of TEMPO as a mild oxidant that selectively oxidizes the reaction intermediates through its multiple reactivity modes, thus facilitating the individual steps to proceed in succession. More than 70 substrate combinations are disclosed, demonstrating the reliability of this protocol to synthesize structurally diverse products, including marketed drugs, drug candidate, and natural products that are unattainable by the existing methods.

1,2-Aryl Migration Induced by Amide C-N Bond-Formation: Reaction of Alkyl Aryl Ketones with Primary Amines Towards α,α-Diaryl β,γ-Unsaturated γ-Lactams

Rearrangement reactions incorporated into cascade reactions play an important role in rapidly increasing molecular complexity from readily available starting materials. Reported here is a Cu-catalyzed cascade reaction of α-(hetero)aryl-substituted alkyl (hetero)aryl ketones with primary amines that incorporates an unusual 1,2-aryl migration induced by amide C-N bond formation to produce a class of structurally novel α,α-diaryl β,γ-unsaturated γ-lactams in generally good-to-excellent yields. This cascade reaction has a broad substrate scope with respect to primary amines, allows a wide spectrum of (hetero)aryl groups to smoothly undergo 1,2-migration, and tolerates electronically diverse α-substituents on the (hetero)aryl ring of the ketones. Mechanistically, this 1,2-aryl migration may stem from the intramolecular amide C-N bond formation which induces nucleophilic migration of the aryl group from the acyl carbon center to the electrophilic carbon center that is conjugated with the resulting iminium moiety.

Vinylidenation of Organoboronic Esters Enabled by a Pd-Catalyzed Metallate Shift

Organoboron "ate" complexes undergo a net vinyl insertion reaction to give 1,1-disubstituted alkenyl boronic esters when treated with stoichiometric allyl acetate and a palladium catalyst. Reactions that employ vinyllithium afforded good to excellent yields after one hour, while reactions that employ vinylmagnesium chloride furnished modest to good yields after 18 hours.

Platinum-Catalyzed Desaturation of Lactams, Ketones, and Lactones

The development of a general platinum-catalyzed desaturation of N-protected lactams, ketones, and lactones to their conjugated α,β-unsaturated counterparts is reported. The reaction operates under mildly acidic conditions at room temperature or 50 °C. It is scalable and tolerates a wide range of functional groups. The complementary reactivity to the palladium-catalyzed desaturation is demonstrated in the efficient conversion of iodide, bromide, and sulfur-containing substrates.

Direct Palladium-Catalyzed β-Arylation of Lactams

A direct and catalytic method is reported here for β-arylation of N-protected lactams with simple aryl iodides. The transformation is enabled by merging soft enolization of lactams, palladium-catalyzed desaturation, Ar-X bond activation, and aryl conjugate addition. The reaction is operated under mild reaction conditions, is scalable, and is chemoselective. Application of this method to concise syntheses of pharmaceutically relevant compounds is demonstrated.

Allyl-Palladium-Catalyzed α,β-Dehydrogenation of Carboxylic Acids via Enediolates

A highly practical and step-economic α,β-dehydrogenation of carboxylic acids via enediolates is reported through the use of allyl-palladium catalysis. Dianions underwent smooth dehydrogenation when generated using Zn(TMP)₂ ⋅2 LiCl as a base in the presence of excess ZnCl₂ , thus avoiding the typical decarboxylation pathway of these substrates. Direct access to 2-enoic acids allows derivatization by numerous approaches.