Regioselectivity in the syntheses of Enantiopure 2-Benzopyrans through Intramolecular cyclization of tethered Lactaldehydes. Conformations of the products

Aggarwal, R., Birkbeck, A.A., Giles, R.G.F., Green, I.R., Gruchlik, Y. and Oosthuizen, F.J. (2003) Regioselectivity in the syntheses of Enantiopure 2-Benzopyrans through Intramolecular cyclization of tethered Lactaldehydes. Conformations of the products. Australian Journal of Chemistry, 56 (5). pp. 489-498.

Abstract

Using titanium tetraisopropoxide, the enantiopure tethered lactaldehyde (α′ S,2S)-2-(3′-hydroxy-α′-methyl-benzyloxy)propanal (6) is cyclized with complete regio- and diastereoselectivity ortho to the phenolic hydroxyl group to give (1S,3S,4R)-3,4-dihydro-1,3-dimethyl-2-benzopyran-4,5-diol (7). Similar cyclization of the epimeric (α′ R,2S)-lactaldehyde (25) yields solely the corresponding (1R,3S,4R)-4,5-diol (34). The 4,5-diacetate (26), but not (35), undergoes conformational inversion of the heterocyclic ring through significant 4,5-peri interactions between the adjacent acetoxy substituents. Spontaneous cyclizations of the corresponding phenoxide ions of the lactalde-hydes (6) and (25), generated by fluoride from their silyl ethers, led to the related 4,7-diols with high regioselectivity through ring-closure para to the aromatic oxygen.

Item Type:	Journal Article
Murdoch Affiliation(s):	School of Chemical and Mathematical Science
Publisher:	Commonwealth Scientific and Industrial Research Organization Publishing
Copyright:	© 2003 CSIRO
URI:	http://researchrepository.murdoch.edu.au/id/eprint/35532

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