Stereoselective Isomerizations of 4-(2′-Chloro-3′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes: Stereochemistry and Conformation of the Product 2-Benzopyrans

Robin G. F. Giles; Ivan R. Green; Shuk-Hui Li

doi:10.1071/CH05120

RESEARCH ARTICLE

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Stereoselective Isomerizations of 4-(2′-Chloro-3′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes: Stereochemistry and Conformation of the Product 2-Benzopyrans

Robin G. F. Giles ^A ^C , Ivan R. Green ^B and Shuk-Hui Li ^A

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, Murdoch University, Murdoch WA 6150, Australia.

^B Department of Chemistry, University of the Western Cape, Bellville 7530, South Africa.

^C Corresponding author. Email: R.Giles@murdoch.edu.au

Australian Journal of Chemistry 58(8) 565-571 https://doi.org/10.1071/CH05120
Submitted: 19 May 2005 Accepted: 2 July 2005 Published: 31 August 2005

Abstract

Stereoselective isomerization of rel-(2R,4S,5R)-4-(2′-chloro-3′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolane 5 with titanium(iv) chloride afforded solely rel-(1R,3R,4S)-5-chloro-4-hydroxy-6-methoxy-1,3-dimethyl-2-benzopyran 17 in high yield in which the conformation adopted by the dihydropyran ring minimized peri-interactions through stereochemistries that were axial for the C-3 methyl, pseudoaxial for the C-4 hydroxy and pseudoequatorial for the C-1 methyl groups. Similar isomerization of the individual rel-(2S,4R,5R)- and rel-(2R,4R,5R)-diastereoisomeric dioxolanes 6 and 7 gave solely the corresponding rel-(1S,3R,4R)-2-benzopyran 25 in which the orientations of the substituents at C-3, C-4 and C-1 were equatorial, pseudoaxial and pseudoequatorial respectively. These observations differed significantly from those previously made for the related isomerizations of the corresponding 4-(2′-chloro-5′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes.

Acknowledgements

Financial support from the Senate of Murdoch University is gratefully acknowledged.

References

Stereoselective Isomerizations of 4-(2′-Chloro-3′-methoxyphenyl)-2,5-dimethyl-1,3-dioxolanes: Stereochemistry and Conformation of the Product 2-Benzopyrans

Abstract

Acknowledgements

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