Gold‐Catalyzed Cascade Friedel–Crafts/Furan‐Yne Cyclization/Heteroenyne Metathesis for the Highly Efficient Construction of Phenanthrene Derivatives

Abstract

A rapid access to highly substituted phenanthrenyl ketones through gold-catalyzed cyclization of 1,6-diyn-4-en-3-ols with furans has been developed. Gold catalysts are effective to catalyze three cascade processes involving Friedel-Crafts/ furan-yne cyclization/heteroenyne metathesis through C À O bond and alkyne activation. This method offers several advantages such as high selectivities and easily accessible starting materials.

Gold‐Catalyzed Cascade Cyclizations of 1,6‐Diynyl Carbonates to Benzo[b]fluorenes Involving Arylation of Oxocarbenium Ion Intermediates and Decarboxylative Etherification

“…found that the acyl group on the oxonium ion b produced through exo ‐cyclization could be trapped intramolecularly by the nucleophilic CAu bond, thereby resulting in a 1,5‐migration of the acyl group (Scheme ) 6. During our ongoing research on gold‐catalyzed cascade reactions7 of 1,6‐diyn‐4‐en‐3‐ols,7a we envisioned that it is possible for oxocarbenium ions a or b to further react with a nucleophile owing to their high electrophilicities. Such transformations should be highly dependent on the stability of the oxocarbenium ion 8.…”

Gold‐Catalyzed Cyclization of 1,6‐Diyne‐4‐en‐3‐ols: Stannyl Transfer from 2‐Tributylstannylfuran Through Au/Sn Transmetalation

“…Recently, we developed a highly efficient gold‐catalyzed cascade reaction between 1,6‐diyne‐4‐en‐3‐ols and furans to give phenanthryl ketones; the reaction involved a Friedel—Crafts alkylation, furan‐yne cyclization, and a heteroenyne metathesis reaction 14a. Interestingly, when 2‐tributylstannylfuran was used as the furan component, and the reaction was conducted in dichloroethane for a period of 1.5 hours, in the presence of 5 mol % of [(PPh 3 )AuCl] and 5 mol % of AgSbF 6 , diyne 1 a was not converted into the expected phenanthrene.…”

Grignard Reagent Acceleration of the Intramolecular Diels–Alder Reaction of Furans with Unactivated Alkynes: Towards Structurally Complex Oxabicyclic Alkenes

“…During the course of our studies into the gold‐catalyzed furan/yne cyclization reaction,5b,c we occasionally found that the reaction of furan‐2‐yl[2‐(phenylethynyl)phenyl]methanone 1 a with a Grignard reagent afforded oxabicycle 3 a in a one‐pot procedure. The optimization results for this reaction are summarized in Table 1.…”