SnCl4–I2 mediated regioselective 6-endo- and 5-exo-cyclization of ortho-allylenols

Author:

Majumdar K C,Biswas A,Mukhopadhyay P P

Abstract

3-Allyl-4-hydroxycoumarins and 4-allyl-3-hydroxycoumarins are obtained in 90%–92% yields by the thermal [3,3] sigmatropic rearrangement of the corresponding ethers. 3-Allyl-4-hydroxy-6-methylpyrone is obtained from the direct alkylation of 4-hydroxy-6-methylpyrone with allyl halide. These substrates on treatment with SnCl4–I2 at 25 °C give a mixture of both 5-exo- and 6-endo-cyclization products. However, regioselective formation of 5-exo products is observed when the reactions are conducted at lower temperatures (0–5 °C, kinetically controlled), while the reaction at a higher temperature (50 °C, thermodynamically controlled) affords regioselectively 6-endo cyclization products.Key words: stannic chloride, iodine, claisen rearrangement, 6-endocyclization, 5-exocyclization, kinetically controlled reaction, thermodynamically controlled reaction.

Publisher

Canadian Science Publishing

Subject

Organic Chemistry,General Chemistry,Catalysis

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