Abstract
Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.
Highlights
The development of general, catalytic and selective procedures for benzyl alcohol C-O bond activation is highly desirable and would constitute a broadly applicable set of transformations in organic synthesis [1]
When compounds 1a–3a were treated with TAFF/MW at 85 °C (100 W) until the disappearance of the starting material after 1.50 min, the corresponding cyclic trimers, namely cyclotripiperonylene (1b, CTP, 85%), cyclotriveratrylene
We investigated the reactivity of 2-methylbenzyl alcohol (5a), which generated benzyl oligomers 5c–f when the reaction was performed under MW conditions and benzyl ethers oligomers
Summary
The development of general, catalytic and selective procedures for benzyl alcohol C-O bond activation is highly desirable and would constitute a broadly applicable set of transformations in organic synthesis [1]. Oligotoluenes are of industrial interest due to their application as insulating oils in high-voltage electrical devices [22], as reagents in the production of termiticide emulsions that demonstrate good penetration and emulsion stability [23] and as reagents in the preparation of corrosion-protection products [24] The synthesis of these compounds has been developed following two different strategies: (a) from a mixture of toluene and benzyl chloride under ultrasound (20 MHz, 6 h) and thermal energy conditions (105 °C, 2 h) [5,6] or (b) from benzyl alcohol with carbon disulfide [2] or dichloromethane [3] used as solvents. Both processes were performed in the presence of bentonitic clay
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