Rapid Access to Oxa‐Bridged Bicyclic Skeletons through Gold‐Catalyzed Tandem Rearrangement Reaction

Copper-Catalyzed Asymmetric Diyne Cyclization via [1,2]-Stevens-Type Rearrangement for the Synthesis of Chiral Chromeno[3,4-c]pyrroles

Here, we report a copper-catalyzed asymmetric cascade cyclization/[1,2]-Stevens-type rearrangement via a non-diazo approach, leading to the practical and atom-economic assembly of various valuable chiral chromeno[3,4-c]pyrroles bearing a quaternary carbon stereocenter in generally moderate to good yields with wide substrate scope and excellent enantioselectivities (up to 99 % ee). Importantly, this protocol not only represents the first example of catalytic asymmetric [1,2]-Stevens-type rearrangement based on alkynes but also constitutes the first asymmetric formal carbene insertion into the Si-O bond.

FeTPPCl/FeCl3 Co-Catalyzed One-Pot Green Synthesis of α-Diaryl-β-alkynol Derivatives via Propargylic Carbocation Chemistry

A green and highly efficient one-pot method for α-diaryl-β-alkynol derivatives in water at room temperature was developed using the cocatalysis of a Lewis acid and meso-tetraphenylporphyrin iron(III) chloride (FeTPPCl). The unprecedented transformation was promoted by a modulation of the charge properties of propargylic carbocation chemistry and the use of an in situ-generated oxonium ylide as a matching nucleophile. The reaction was performed in water at room temperature with a highly step-economic manipulation in good to excellent yields and with a broad substrate scope. Water also acts as the third reactant for the one-pot transformation. Notably, the FeTPPCl catalyst can be directly reused four times with a slight discount in yields.

Consecutive O-S/N-S Bond Cleavage in Gold-Catalyzed Rearrangement Reactions of Alkynyl N-Sulfinylimines

Gold-catalyzed reactions of alkynyl N-sulfinylimines were used to produce the corresponding 2H-azirines possessing sulfenyl and acyl groups at the 3-position of the azirine ring in good to excellent yields. These reactions involved internal transfer of the sulfinyl oxygen atom to form a thiooxime intermediate tethered to an α-oxo gold carbene moiety. Subsequent insertion of the carbene into the N-S bond resulted in ring construction.

Assessing counterion effects in gold-catalyzed domino spirocyclization: an industrial perspective on hydrogen bonding

We herein report a computational study of the hydrogen bonding in gold-catalyzed ipso-cyclization to diverse polyheterocyclic frameworks. The different roles of these hydrogen bonds are analyzed for the different ipso-cyclization reactions. The fine-tunability of the electronic as well as steric properties of gold counterions contributed substantially to the popularity of the dearomatization reaction, with robust applications in total synthesis and gold catalysis. We have found correlation between the hydrogen bonding parameters and chemoselectivity in gold-catalyzed spirocyclization, playing critical roles in determining the reaction direction of counterion-based enantioselective gold catalysis. The expanded use of counterions via hydrogen bonding interaction can occupy an important role in the future concerning catalyst optimization in gold catalysis.

Cooperative Catalysis for the Highly Diastereo- and Enantioselective [4+3]-Cycloannulation of ortho-Quinone Methides and Carbonyl Ylides

We describe herein a highly diastereo- and enantioselective [4+3]-cycloannulation of ortho-quinone methides and carbonyl ylides to furnish functionalized oxa-bridged dibenzooxacines with excellent yields and stereoselectivity in a single synthetic step. The combination of rhodium and chiral phosphoric acid catalysis working in concert to generate both transient intermediates in situ provides direct access to complex bicyclic products with two quaternary and one tertiary stereogenic centers. The products may be further functionalized into valuable and enantiomerically highly enriched building blocks.

Construction of polycyclic bridged indene derivatives by a tandem 1,3-rearrangement/intramolecular Friedel-Crafts cyclization of propargyl acetates

An unprecedented Lewis acid-catalyzed cascade 1,3-rearrangement/Friedel-Crafts cyclization of propargyl acetates is developed for the construction of polycyclic bridged indene derivatives in moderate to good yields. This practical procedure features mild conditions, broad substrate scope, and easy operation.