“…Examples are known in phosphorus stereochemistry, e.g., hydrogen chloride catalyzed epimerization of 9-phenyl-9-phosphabicyclo [4.2.1 ]nonatriene,47 lithium aluminum hydride catalyzed epimerization of 3A (which is faster than reduction),48 and base-catalyzed epimerization of 8 (which is faster than hydrolysis). 49 In all three examples, stereomutation may be rationalized by attack of X (formally, Cl-, H-, and OH-, respectively), followed by three pseudorotations and loss of X. This can be readily visualized by reference to Figure 5.…”
“…Examples are known in phosphorus stereochemistry, e.g., hydrogen chloride catalyzed epimerization of 9-phenyl-9-phosphabicyclo [4.2.1 ]nonatriene,47 lithium aluminum hydride catalyzed epimerization of 3A (which is faster than reduction),48 and base-catalyzed epimerization of 8 (which is faster than hydrolysis). 49 In all three examples, stereomutation may be rationalized by attack of X (formally, Cl-, H-, and OH-, respectively), followed by three pseudorotations and loss of X. This can be readily visualized by reference to Figure 5.…”
“…These contrast with the inversion of configuration observed with acyclic alkoxyphosphonium salts. 143 Lack of stereospecificity 144 or the preferential formation of one isomer, as in eq 40, 145 can be observed if pseudorotation is fast compared to the elimination step or if substituents with comparable apicophilicity are bound to phosphorus. This means that studies on the product distribution and isomer ratios obtained in targeted substitution reactions made it possible to determine an order of kinetic apicophilicity for a number of common functionalities.…”
Section: Stereochemistry Of the Nucleophilic Substitutions On Phosphe...mentioning
confidence: 99%
“…Lack of stereospecificity or the preferential formation of one isomer, as in eq 40, can be observed if pseudorotation is fast compared to the elimination step or if substituents with comparable apicophilicity are bound to phosphorus. …”
Section: Stereochemistry Of the Nucleophilic Substitutions On
Phosphe...mentioning
“…In cyclic systems, however, ring size has been implicated as having a pronounced effect on the steric course of the nucleophilic displacement of exocyclic substituents at phosphorus. Phosphetanium salts have been shown to be converted to the corresponding phosphine oxides with complete retention of configuration at phosphorus . On the other hand, depending on the specific compound, phospholanium salts have been observed to cleave with complete retention of configuration or to produce mixtures of stereoisomers .…”
[reaction: see text] The synthesis of pure cis- and trans-3-methoxy-2,2,6-trimethyl-3-phenyl-1,3-oxaphosphorinanium tetrafluoroborate salts 3a and 3b, respectively, molecules designed to evaluate the effect of oxygen on the steric course of base-induced nucleophilic displacement of the methoxy group at phosphorus, was accomplished. It was found that these isomeric salts react with aqueous sodium hydroxide to produce the corresponding phosphine oxides 7a and 7b with complete retention of configuration at phosphorus.
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