Mechanistic and Exploratory Investigations into the Synthesis of 1,3,5-Triaroylbenzenes from 1‑Aryl-2-propyn-1-ones and 1,3,5-Triacetylbenzene from 4‑Methoxy-3-buten-2-one by Cyclotrimerization in Hot Water in the Absence of Added Acid or Base

Neat 1-phenyl- and 1-(<i>p</i>-tolyl)-2-propyn-1-ones (<b>1</b> and <b>1</b>′, respectively) were heated in water without any additive at 150 °C for 2 h to give 1,3,5-tribenzoyl- and 1,3,5-tri-(<i>p</i>-toluoyl)­benzenes (<b>2</b> and <b>2</b>′, respectively) in 74 and 52% yields, respectively. The crossed reactions of <b>1</b> with the enolate of <i>p</i>-toluoylacetaldehyde (<b>3</b>′) and <b>1</b>′ with the enolate of benzoylacetaldehyde (<b>3)</b> were carried out to give unsymmetrically substituted 1-toluoyl-3,5-dibenzoylbenzene (Ph₂Tol) and 1,3-ditoluoyl-5-benzoylbenzene (PhTol₂), respectively, corroborating the previously proposed reaction mechanism in which <b>3</b> and <b>3</b>′ that are formed by rate-determining nucleophilic attack of HO^– on <b>1</b> and <b>1</b>′ or its conjugate acids formed by subsequent protonation would serve as a common intermediate for the formation of <b>2</b>, <b>2</b>′ and the acetophenone derivatives as byproducts. When 4-methoxy-3-buten-2-one (<b>4</b>) was heated in hot pure water without any additive at 150 °C for 30 min, 1,3,5-triacetylbenzene (<b>5</b>) was obtained in an isolated yield of 77% just by removing water by filtering the crystalline product from the cooled reaction mixture. The reaction did not take place in the absence of water. Slow decompositions of <b>5</b> in water set in at the temperature of 300 °C for 30 min

Ring-Opening Reactions of α- and β‑Pinenes in Pressurized Hot Water in the Absence of Any Additive

Reactions of α- and β-pinenes in pressurized hot water were examined in a batch reactor made of a SS316 1/2-in. tube at temperatures of 250–400 °C, pressures of 4–30 MPa, and reaction times of 1–30 min in the absence of any additive under an argon atmosphere. The maximum yields of limonene from α-pinene were ca. 70% in 20 min at 300 °C or 1 min at 400 °C. Limonene was obtained from β-pinene in ca. 16% yield for 30 min at 300 °C and 1 min at 400 °C. Reversible production of myrcene in 14% yield and formation of unidentified C₂₀ dimer fractions were noted for 1 min at 370 °C from β-pinene. The conversion of α-pinene to limonene took place under anhydrous conditions, albeit at slightly lower yield of 65% compared to processes conducted in the presence of water, where increased limonene yield of 70% was observed for 1 min at 400 °C. The conversion of β-pinene to limonene under anhydrous conditions was limited to 6.1% in contrast to 11.9% in the presence of water for 7 min at 370 °C. In the presence of oxygen, <i>p</i>-cymene was formed in 23% and 24% yield at the expense of limonene from α- and β-pinenes, respectively, for 30 min at 400 °C