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On the Reactivity and Selectivity of Galacturonic Acid Lactones
- Source :
- European Journal of Organic Chemistry. 2012:5729-5737
- Publication Year :
- 2012
- Publisher :
- Wiley, 2012.
-
Abstract
- The reactivity and stereoselectivity of a galacturonic acid 3,6-lactone thioglycosyl donor, previously described as a highly reactive glycosylating agent, has been investigated by using a series of competition experiments and condensation reactions with different thiophilic activator systems. It is revealed that the relative reactivity of the thioglycosides depends on the activator system used and that p-nitrophenylsulfenyl triflate shows overall attenuated reactivity differences with respect to the commonly used N-iodosuccinimide/triflic acid promoter system. With respect to the stereoselectivity of the studied galacturonic acid 3,6-lactone thioglycosyl donor, it is revealed that a preactivation-based glycosylation system gives rise to α-selective glycosylation, whereas an in situ activation protocol leads to the formation of the β-product with good selectivity. It is hypothesized that these opposingstereoselectivities are the result of different product-forming intermediates. Where preactivation of the donor leads to the formation of an intermediate β-triflate, which is substituted in a concerted fashion to provide the α-product, a 3H4 oxocarbenium ion like species is substituted in the in situ activation experiment to provide the β-linked product.
Details
- ISSN :
- 1434193X
- Volume :
- 2012
- Database :
- OpenAIRE
- Journal :
- European Journal of Organic Chemistry
- Accession number :
- edsair.doi...........60c97aa9f4c3844f0044572a852a1d0e