A new method for the formation of anti-apicophilic (O-cis) spirophosphoranes - Kinetic studies on the stereomutation of O-cis arylspirophosphoranes to their O-trans isomers

摘要

P-H spirophosphorane 4 bearing two Martin ligands was converted to dianions (5a-n), bearing R groups, with excess organolithium reagents (RLi). Subsequent oxidation with 12 at ambient temperature gave anti-apicophilic (O-cis) spiro-phosphoranes 2a-n. All anti-apicophilic phosphoranes 2a-n isomerized irreversibly to the O-trans spirophosphoranes 3a-n, respectively. For 2,6-dialkylphenyl derivatives 2k-n, the barrier for pseudorotation between enantiomers 2-R-P and 2-S-P was rather high, and thus the interconversion could not be observed on the NMR timescale. The activation parameters for the pseudorotation of the triisopropylphenyl (TIP) derivative 2n to 3n were almost identical with those of nBu derivative 2b to 3b, i.e., Delta H-double dagger = 21.3 kcal mol(-1), Delta S-double dagger: = -9.4 eu.