Rh-Catalyzed [3+2] Annulation of Cyclic Ketimines and Alkynyl Chloride: A Strategy for Accessing Unsymmetrically Substituted and Highly Functionalizable Indenes

A palladium-catalyzed synthesis of cyclic alkenyl boronates from alkenyl chlorides

A palladium-catalyzed borylation of cyclic alkenyl chlorides with B2pin2 is reported. This transformation allows for the conversion of diverse cyclic alkenyl chlorides into synthetically versatile alkenyl boronates with moderate to excellent yields. The utility of this reaction has been demonstrated with practical Suzuki-Miyaura coupling and aziridination reactions, which allow access to functionalized olefins and valuable boron-substituted aziridines.

Synthesis of spiropyrans via Ru(II)-catalyzed coupling of 3-aryl-2H-benzo[b][1,4]oxazines with benzoquinones

An efficient Ru(II)-catalyzed C-H activation-based spiroannulation of benzoxazines with the easily available benzoquinone and N-sulfonyl quinone monoimine has been realized, providing a straightforward strategy to access NH-containing spiropyrans in moderate to good yields with good functional group compatibility. The procedure features atom- and step-economy, mild conditions, and excellent chemoselectivity. Moreover, a catalytically competent five-membered cycloruthenated complex has been isolated.

Straightforward Access to Free β2,3,3 -Amino Acids through One Pot C-H Activation/C-C Cleavage

The first synthesis of unnatural β2,3,3 -amino acids with a spirocyclic backbone by one-pot protocol has been presented. This reaction features wide functional group tolerance and feasibility of post-functionalization of natural products and biologically important molecules. Novel dipeptide and tripeptide structures were assembled using this newly developed β2,3,3 -amino acid in high efficiency. The combination of C-H activation and C-C cleavage for the synthesis of β-amino acids would trigger more promising synthetic routes for this compound.

Palladium-Catalyzed Tandem Cyclization of Bromoalkynes, Anilines and CO: Access to 1,3-Substituted Maleimides

A novel palladium-catalyzed three-component carbonylation reaction for the assembly of various 1,3-substituted maleimide derivatives from haloalkynes and simple anilines. The nucleophilic addition reaction of haloalkynes, anilines and CO, and insertion of carbonyl have been achieved sequentially in this reaction. The high chemo- and regioselectivities, as well as no need of expensive ligands or additives further illustrate the synthetic value of this approach.

Rhodium(III)-catalyzed intermolecular [3+3] annulation of benzoxazines with quinone compounds: access to spiro-heterocyclic scaffolds

A rhodium(III)-catalyzed redox-neutral spiroannulation approach to access the spiro[benzo[b][1,4]oxazine-benzo[c]chromene skeleton is described in this contribution. A variety of spiro[5.5]-heterocyclic scaffolds were obtained in moderate to excellent yields under mild conditions. Key features of this protocol are good substrate scope, silver-free conditions, low catalyst loadings, easy handling under air and 100% atom economy. Furthermore, scale-up reactions and late-stage derivatizations highlight the potential synthetic utility of this methodology.

Rh(III)-catalyzed [3 + 2] spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates through ortho-C-H bond functionalization

Rhodium(III)-catalyzed [3 + 2]-spiroannulation of 2-aryl-1,4-benzoxazines with 4-hydroxy-2-alkynoates has been developed for the synthesis of highly rigid spirolactones in good yields with high regioselectivity. The reaction proceeds through a cascade of C-H activation followed by C-H annulation and lactonization. In this approach, two C-C and C-O bonds are formed in a single step. This is the first report on the spiroannulation of 2,3-dihydro-1,4-benzoxazines with 4-hydroxy-2-alkynoates.

Synthesis of indene-fused spiro-dibenz(ox)azepines via Rh(III)-catalyzed cascade regioselective C-H activation/annulation

We report an unprecedented atom-economic one-pot Cp*Rh(III)-catalyzed regioselective [3+2]-spiroannulation reaction between dibenz(ox)azepines and ynones, allowing the synthesis of biologically relevant novel spirocyclic dibenz(ox)azepines under operationally simple and mild reaction conditions. The reaction proceeds without any silver additive or external oxidant implementing a redox-neutral pathway. A broad substrate scope with diverse functional group tolerance permitted the regioselective synthesis of a wide spectrum of indene-containing spirocyclic dibenz(ox)azepines in good to excellent yields. Also, we showcased detailed mechanistic studies to justify the formation of spirocycles. In addition, the synthetic utility of this process was also demonstrated by the modular synthesis of various steroid conjugates.