TITLE

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

AUTHOR(S)
Majumdar, K. C.; Biswas, A.; Mukhopadhyay, P. P.
PUB. DATE
December 2005
SOURCE
Canadian Journal of Chemistry;Dec2005, Vol. 83 Issue 12, p2046
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
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.
ACCESSION #
20454169

 

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