Abstract
SmCl3 (20 mol%) has been used as an efficient catalyst for reaction between aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione at 120°C to give 1,8-dioxo-octahydroxanthene derivatives in high yield. The same reaction in water, at room temperature gave only the open chain analogue of 1,8-dioxo-octahydroxanthene. Use of eco-friendly green Lewis acid, readily available catalyst and easy isolation of the product makes this a convenient method for the synthesis of either of the products.
Highlights
SmCl3 (20 mol%) has been used as an efficient catalyst for reaction between aromatic aldehydes and 5,5-dimethyl1,3-cyclohexanedione at 120°C to give 1,8-dioxo-octahydroxanthene derivatives in high yield
Considering that there is a need for the use of more useful greener acid catalyst we examined SmCl3, a water resistant, reusable, lanthanide Lewis acid for the synthesis of 1,8-dioxo-octahydroxanthenes
Heating the neat reaction mixture in presence of SmCl3 (20 mol%) at 120°C for 8 h, led to the formation of cyclised product 4d in excellent yield. Based on these results it was concluded that use of SmCl3 (10 mol %) in water, at room temperature and SmCl3 (20 mol %) without solvent at 120°C would be the useful conditions for the formation of open chain compound 3d and the 9-phenyl1,8-dioxo-octahydroxanthane (4d) respectively
Summary
Reaction between 4-NO2-benzaldehyde (1d, 1 mole) and dimedone (2, 2 mole) in presence of SmCl3 was identified as the test reaction and different reaction parameters were studied for the formation of corresponding 1,8-dioxo-octahydroxanthene. Considering the fact that SmCl3 is a water resistant Lewis acid the reaction was carried out in water at room temperature (RT). The reaction was complete in 15 min. It was only, the open chain, compound 2,2’-((4-nitrophenyl)methylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-enone)
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