text: A typical Danheiser benzannulation reaction is run with a 0.4-2.0 M solution of the cyclobutenone in toluene heated at 80-160 °C with a slight excess of the cyclobutenone. Upon addition of the alkyne a [2+2] cycloaddition occurs. The crude annulation product is treated with 10% potassium hydroxide in methanol to saponify the ester side product formed from the reaction of the phenolic product with excess vinylketene (Scheme 6). 
  For the second generation reaction starting with the diazoketone, the reaction is performed by irradiation of a 0.7 M solution of the ketone with 1.0-1.2 equivalents of acetylene. A low-pressure mercury-vapor lamp at 254 nm in a photochemical reactor is used for 5–8 hours until all the diazoketone has been consumed as determined by TLC analysis. Dichloromethane, chloroform, and 1,2-dichloroethane, are all appropriate solvents for the annulation reaction.