Acetylenchemie, 10. Mitt.: Cycloisomerisierung von 3-Acetyl-3-(prop-2-inyl)-indol-2-on zum 3-Acetyl-2-methyl-2H-furo[2,3-b]indol Acetylenic Chemistry, Part 10: Cycloisomerisation of 3-Acetyl-3-(prop-2-inyl)-indole-2-one to 3-Acetyl-2-methyl-2H-furo[2,3-b]indole