Flexible and Practical Synthesis of Anthracenes through Gold-Catalyzed Cyclization of o-Alkynyldiarylmethanes

Abstract

A concise gold-catalyzed method for the preparation of anthracenes from o-alkynyldiarylmethanes has been developed. Under mild reaction conditions, versatile anthracene derivatives were formed in moderate to good yields. The high flexibility, broad substrate scope, and mild nature of this reaction render it a viable alternative for the synthesis of anthracenes.

Gold‐Catalyzed 6‐Exo‐Dig Cycloisomerization: A Versatile Approach to Functionalized Phenanthrenes

“…These results indicated that path a should be the main pathway of the reaction, although the formation of intermediate A could not be detected by monitoring the cyclization reaction by 1 H NMR spectroscopy under the optimized reaction conditions (Table 1, entry 8). Notably, similar to our previously reported results,9a part of 2 a might be generated via path b involving a gold‐catalyzed hydration and subsequent acid‐catalyzed cyclodehydration (Table 4, entries 2–3), which may also explain the role of acid here to accelerate the minor pathway.…”

“…Next, a variety of gold catalysts were investigated (Table 1, entries 1–9), and [(C 6 F 5 ) 3 PAuNTf 2 ] was found to be the best among them (Table 1, entry 8). Notably, similar to our previously reported protocol,9a the main byproduct here was methyl ketone 3 a formed by a gold‐catalyzed hydration reaction. In addition, PtCl 2 and AgNTf 2 only led to poor results (Table 1, entries 10–11).…”

“…5a Recently, Kim and co‐workers reported an elegant protocol for the synthesis of functionalized phenanthrenes involving an In III ‐catalyzed 6‐ exo ‐ dig cycloisomerization 8. In our recent study toward a gold‐catalyzed cycloisomerization reaction,9 we reported a gold‐catalyzed 6‐ exo ‐ dig cycloisomerization of o ‐alkynyldiarylmethanes to prepare versatile anthracenes 9a. Inspired by these results, we envisioned that the synthesis of phenanthrenes 2 might be accessed through the gold‐catalyzed 6‐ exo ‐ dig cycloisomerization reaction of o ‐propargylbiaryls 1 (Scheme ) 10.…”

“…Propargylbiphenyl 1 a was chosen as a model substrate for our initial study, and some of the results are listed in Table 1. The catalytic potential of the gold complex [Et 3 PAuNTf 2 ] was first evaluated given its previously reported high activity for the conversion of o ‐alkynyldiarylmethanes into anthracenes 9a. To our delight, upon exposure of 1 a to 5 mol % [Et 3 PAuNTf 2 ] at room temperature, the reaction could indeed give the desired phenanthrene 2 a , albeit in low yield after 24 h (Table 1, entry 1).…”

Regioselective Annulation of Unsymmetrical 1,2‐Phenylenebis(diaryl/diheteroarylmethanol): A Facile Synthesis of Anthracene, Tetracene, and Naphtho[b]thiophene Analogues

“…In recent years, the Lewis acid/Brønsted acid mediated domino reaction has been successfully applied for the synthesis of a wide variety of π‐conjugated heterocycles 15. Shu et al reported16 the synthesis of substituted anthracenes by gold‐catalyzed intramolecular cyclization of orthoalkynyl‐diarylmethanes. Matsuo and co‐workers achieved17 the synthesis of anthracenes from diarylmethanes through a Bradsher‐type reaction that involved formylation of the aryl unit followed by Lewis acid catalyzed Friedel–Crafts intramolecular cyclization reaction.…”