The material is commercially available from Sigma-Aldrich and not very expensive. It may be more cost effective to just buy it. catalog M46209 - 1,3,3-Trimethyl-2-methyleneindoline
You should check other suppliers besides Sigma-Aldrich such as Alfa Aesar A16741 1,3,3-Trimethyl-2-methyleneindoline, 95% 250grams for $82.24 USD or Acros Organics 421942500 1,3,3-Trimethyl-2-methyleneindoline, Fischers base, 98.5%, 250 GR, $95.77 USD. Use a search engine like Chemexper https://www.chemexper.com to search for an inexpensive local source for the chemical.