STEREOELECTRONIC EFFECTS IN THE HYDROLYSIS OF PHOSPHONIUM IONS FROM ACYCLIC AND BICYCLIC PHOSPHOROTHIONATES
- 1 January 1990
- journal article
- research article
- Published by Taylor & Francis in Phosphorus, Sulfur, and Silicon and the Related Elements
- Vol. 47 (1) , 93-104
- https://doi.org/10.1080/10426509008046849
Abstract
The alkaline hydrolysis of the bicyclic phosphonium ion 1-methyl-3,5,8-trioxabicyclo-[2,2,2]octane-4-methylthiophosphonium ion 1 proceeds mainly with P-O bond cleavage as shown by hydrolysis in 18O labeled water to form the cyclic epimers cis- and trans-2-methylmercapto-2-oxo-5-hydroxymethyl- l,3,2-dioxaphosphorinane (2/3) in addition to the bicyclic phosphate, l-methyl-4-phospha-3,5,8-trioxabicyclo-(2,2,2]octane-4-oxide, 4. The trans epimer 3 is formed after pseudorotation of the triagonal bipyramid (tbp) intermediate and is the predominant initial product. This could be explained by deprotonation of the initial neutral tbp intermediate 5 followed by fast pseudorotation to give the more stable anionic tbp 5′ in which the negatively charged oxygen is placed in the equatorial position of the intermediate. In contrast, the acyclic analogue triethoxy(methylthio)phosphonium ion undergoes alkaline hydrolysis with 100% P-S bond cleavage. It is very unusual to observe P-O bond cleavage competitive with P-S bond cleavage as we have demonstrated for the hydrolysis of the bicyclic thiophosphonium ion, 1. These results are supportive of the stereoelectronic effect hypothesis.Keywords
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