Brønsted Acid‐Promoted Benzannulation of o‐Alkynylbenzaldehyde and Alkyne, and the Positive Effect of Propargyl Alcohol

Abstract

Bromotrimethylsilane-promoted benzannulation of o-alkynylbenzaldehydes and alkynes to yield 1naphthyl aryl ketones is reported. The reaction conditions are mild, metal-free, and do not require pretreatment/protection of the substrates. We found that aryl propargyl alcohols were very effective substrates for this reaction, compared with other alkynes. Studies on the reaction scope, monitoring the reaction progress by 1 H NMR, and theoretical calculations suggest that isochromenylium (benzopyrilium) ion is the key reaction intermediate.

Gold-Catalyzed Reactions of Enynals with Alkenes for Synthesis Binaphthyl Derivatives

“…Because enynals are easily activated by Lewis acid or diverse transition metal catalysts, they were usually used for constructing naphthalene derivatives and other polycyclic skeletons . In 2003, Yamamoto and co-workers presented a practical protocol for the synthesis of 1,2-dihydronaphthalene, by using enynals and olefins as the reaction substrates, in the presence of Cu­(OTf) 2 (Scheme b) .…”