Stereochemistry of Allylic Rearrangements. XIII. The Racemization, Carboxyl-oxygen Equilibration and Solvolysis of trans-α,γ-Dimethylallyl p-Nitrobenzoate in Aqueous Acetone

Ion Pair Dynamics: Solvolyses of Chiral 1,3-Diarylallyl Carboxylates as a Case Study

“…In line with this analysis, Figures 3 and 4 show an increase of the yields of all isomerization products ((S)-1, (R)-2, and (S)-2) generated during the solvolysis of (R)-1 when the solvent was changed from 60% to 80% and 90% aqueous acetone. In the same way, one can rationalize Goering's observations that the ratio k α /k t (polarimetric rate constant/titrimetric rate constant) for the solvolyses of cis-5-methylcyclohex-2-enyl 2-carboxybenzoate, 26 trans-5-methylcyclohex-2-enyl 4-nitrobenzoate, 27b and 1,3dimethylallyl 4-nitrobenzoate 67 in aqueous acetone generally increased with decreasing water content because of the increasing nucleophilicities of the carboxylate ions. The enhancement of internal return with increasing electrophilicities of the carbenium ions is also in agreement with conclusions of Yabe and Kochi, which were derived from the rates of the recombinations of anthracenylium radical cation−trinitromethide ion pairs generated by laser-flash-induced electron transfer in the anthracene−tetranitromethane complexes.…”

Competing sulfonylation and phosphonylation following rearrangement of an O-sulfonyl-N-phosphinoylhydroxylamine with tert-butylamine: demonstration of a phosphonamidic-sulfonic anhydride intermediate and 18O-labelling evidence on how it may be formed1

“…The two benzylic protons in each of the diastereoisomers of 7 are themselves diastereotopic, and they appear in the 1 H NMR spectrum as an AB quartet centred at δ H 4.60 (major diastereoisomer) or 4. 19.…”

“…the failure of Bu t NH 2 , even at the highest concentration, to suppress anhydride formation (Scheme 1, step c) by intercepting the metaphosphonimidate and taking it directly to the phosphonic diamide product (step aЈ). There are several examples of racemisation and isomerisation in which a carboxylate 19 or sulfonate 20 anion is released and recaptured with only partial equilibration of the oxygen atoms, and at least one example of a more profound rearrangement (migration from N to C) in which the sulfonate oxygen atom released by bond-breaking is preferentially employed in subsequent bond making. 21 In all of these, however, the anion recombines with a cation, not an uncharged species like a metaphosphonimidate.…”