AIMS: The small organic molecular compounds with biological activity containing C-C and C-N or C-O bonding were efficiently prepared without catalyst and solvent in the hydrothermal synthesis reactor. OBJECTIVES: Our goal was to explore new applications for the more environmentally friendly and efficient synthesis of bis(indolyl)methyl, xanthene, quinazolinone, and N-heterocyclic derivatives in hydrothermal synthesis reactors under solvent-free and catalyst-free conditions. METHODS: A greener and more efficient method was successfully developed for the synthesis of bis(indolyl)methyl, heteroanthracene, quinazolinone, and N-heterocyclic derivatives using a hydrothermal synthesis reactor in a solvent- and catalyst-free manner. RESULTS: In a hydrothermal synthesis reactor, bis(indoyl)methyl, xanthene, quinazolinone, and N-heterocyclic derivatives were synthesized without catalysts and solvents. CONCLUSION: Overall, it is proved once again that the catalyst-free and solvent-free synthesis method has universal value and is a more ideal and environmentally friendly new method, especially the hydrothermal reactor for synthesis.