Experimental Tests of the Stereoelectronic Effect at Phosphorus: Nucleophilic Reactivity of Phosphite Esters

Article abstract of DOI:10.1021/ja00337a029

Triethyl phosphite rapidly reacts with ethyl benzenesulfenate or diethyl peroxide to yield pentaethoxyphosphorane.In contrast, 1-methyl-4-phospha-3,5,8-trioxabicyclo<2.2.2>octane (1) fails to react with either electrophile to yield the expected bicyclic phosphorane 5.The poor reactivity of the bicyclic phosphite 1 is due to a kinetic rather than a thermodynamic barrier because 5 is formed smoothly from an equimolar mixture of P(OEt)5 and the triol 1,1,1-tris(hydroxymethyl)ethane.This result is interpreted in terms of the stereoelectronic effect.The order of nucleophilic reactivity of trialkyl phosphites with 3-benzylidene-2,4-pentanedione is also shown to be consistent with the stereoelectronic effect.The bicyclic phosphite 1 reacted 750 times slower than the pseudoequatorial 2-methoxy ester of hexahydrobenzo-1,3,2-dioxaphosphorinane in a Michael addition reaction with 3-benzylidene-2,4-pentanedione.