To obtain information concerning the stereomeric factors that affect the course of replacement reactions, a study has been made of the replacement of the halogen of certain acetyglycosyl bromides by methanol in the presence of silver carbonate (the Koenigs-Knorr reaction). The investigation shows that the solvent and the temperature greatly influence the course of the reaction when the configuration is trans but have little influence when the configuration is cis. The experimental data support the concept that under definite stereomeric conditions a solvated orthoester intermediate takes part in the reaction at low temperatures. At higher temperatures part of the reac tion appears to take place t hrough a free or thoester ion. 'By select ion of suit able experimental conditions, it was pos ible to direct the orthoester reaction in large measure to either t he m ethyl orthoacetate or t he methyl acetyglycoside wi th apparent retention of configuration. C H aO H "'C/ I'" 1 0 Aco-r-I III
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Isbell et al. (1949) studied this question.