a mixture of four compounds is possible. Usually the erythro product 463 was obtained in a 6:4 ratio.

The two examples in Scheme 81 illustrate the use of a cyclic enol ether reacting with anomeric acetate 467 to give 468 [139], as well as the reaction of an olefin with the same acetate to give the novel ring-fused product 469 [140].

The final example demonstrates the use of amino acid derived enol ether 470 reacting with a glycosyl imidate 469 under Lewis acid catalysis to give a low yield of the carbon-linked threonine isostere 471 (Scheme 82) [141].

Scheme 81
Scheme 82
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