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 1‐naphthyl 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. magnified image