New paradigms for the peroxy acid epoxidation of CC double bonds: The role of the peroxy acid s-trans conformer and of the 1,2-H transfer in the epoxidation of cyclic allylic alcohols

Journal of Organic Chemistry

Volumn 69, Issue 22, 2004, Pages 7479-7485

  Freccero, Mauro ^a   Gandolfi, Remo ^a   Sarzi Amadè, Mirko ^a   Rastelli, Augusto ^b  

^a UNIVERSITY OF PAVIA   (Italy)

^b UNIVERSITY OF MODENA AND REGGIO EMILIA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL BONDS; ISOMERS; OLEFINS; OXIDATION;

PEROXY ACID EPOXIDATION; POLAR SOLVENTS;

AROMATIC COMPOUNDS;

2 CYCLOBUTENOL; 2 CYCLOHEXENOL; 2 CYCLOPENTENOL; ACID; ALCOHOL DERIVATIVE; ALLYL ALCOHOL; BENZENE; CARBONYL DERIVATIVE; DICHLOROMETHANE; EPOXIDE; ETHYLENE OXIDE; FORMIC ACID DERIVATIVE; OXYGEN; PERACID; PERFORMIC ACID; UNCLASSIFIED DRUG;

ARTICLE; CALCULATION; CHEMICAL BOND; CHEMICAL STRUCTURE; CIS ISOMER; DIPOLE; EPOXIDATION; REACTION ANALYSIS;

EID: 6344282658     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo048980j     Document Type: Article

References (42)

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21. TSs involving protonated s-trans performic acid were reported by Bach et al. for the acid catalyzed performic acid epoxidation of ethylene. Protonation at the carbonyl oxygen makes the s-trans isomer much more stable than the s-cis one. However, according to authors, protonated peroxy acids do not play any role in peroxy acid epoxidation. Bach, R. D.; Canepa, C.; Winter J. E.; Blanchette, P. E. J. Org. Chem. 1997, 62, 5191.
22. (a) We have recently demonstrated5c by DFT calculations that also highly distorted TSs, formally originating from s-cis performic acid, can enter the 1,2-H shift in preference to the traditional 1,4-H transfer,
23. 2 see, for example: de Visser, S. P.; Kaneti, J.; Neumann, R.; Shaik, S. J. Org. Chem. 2003, 68, 2903.
24. 2. The protic molecule allows a mediated 1,2-H transfer through a cyclic TS. However, Edwards et al. also reported that sulfide oxidations with peroxy acids did not show any kinetic evidence for solvent participation in the transition state in the case of aprotic solvent.1c The latter observation stands in contrast with the recent suggestion by Plesnicar et al. that explains the decreased reactivity of peroxy acids in "basic" solvents as a result of involvement in the transition state of a complex between s-trans peroxy acid and a solvent molecule.1a,7
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27. The meaning of the descriptors used are as follows: cis and trans indicate that the TS formally originates from s-cis and s-trans, respectively, conformer of performic acid; syn and and correspond to attacks by performic acid to the double bond on the same and opposite side, respectively, relative to the hydroxy group; in endo and exo TSs the formate moiety is oriented inside and outside, respectively, relative to the allylic alcohol ring.
28. 2 solution). See also ref 5d for 2-cyclohexenol data.
29. (b) The free energy (at 298.15 K) of TS trans,syn,endo-4a (n = 1) is lower by 7.40 kcal/mol (gas phase) and 6.43 kcal/mol (benzene solution) than that of TS trans,syn,exo-5a (n = 1) at the B3LYP/6-311+G(d,p) level. The latter transition structure is not a stationary point in dichloromethane solution (i.e., all our attempts to locate it led either to starting reactants or to products). Moreover, at the same theory level TS trans,syn,endo-4h (n = 2) resides at lower free energy than TS trans,syn,exo-5b by 8.2 kcal/ mol in gas phase but when optimization was performed at the B3LYP/ level the latter TS collapsed to the corresonding cis,syn,endo TS in which the peroxy acid acts as hydrogen bond donor,
30. 2〉 = 0.066 with the B3LYP/6-311+G(d,p) method].
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34. Bach et al. have demonstrated3e that the concerted synchronous spiro (perpendicular in our notation)18 TS for epoxidation of ethylene is unambiguously supported by high level ab initio and CASSCF calculations. This study convincingly rejects the recent proposal, advanced by Leszczynski et al.16 for the same reaction on the basis of CASSCF calculations, of a planar TS with an unsymmetrical open chain diradical structure. The conclusion by Leszczynski et al. seems to be the result of an artifact of calculations due to an incorrect choice of the active space. In fact, Bach et al. stressed that the choice of active orbitals is critical for the CASSCF approximation and that it is mandatory to recover the effects of dynamic correlation before comparing the total energies of perpendicular and planar TSs.
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37. 7 bond, see 8 in Scheme 2) is close to 90° (that is, larger than 45°)] while in a "planar" TS this angle is close to 0° (smaller than 45°) and the O-H and C=C bonds lie in the same (or almost the same) plane.
38. 2 group is close to 0, slightly positive and negative, respectively, according to NPA and CHELPG methods in both TSs 2 and TSs 4{B3LYP/6-311+G(d,p) calculations, TS 2a: -0.06e (NPA) and +0.09e (CHELPG) in the gas phase and -0.05e (NPA) and +0.08e (CHELPG) in dichloromethane; TS 4a: -0.06e (NPA) and +0.08e (CHELPG) in the gas phase and -0.03e (NPA) and +0.09e (CHELPG) in dichloromethane.
39. Herges, R. Angew. Chem., Int. Ed. Engl. 1994, 33, 255.
40. 2a = 0.84 kcal/ mol, gas phase).
41. -1} at the B3LYP/6-311+G(d,p) level.
42. Aside from TSs cis,anti,exo-6 and trans,anti,endo-7 there are two more alternative TSs for anti attack, namely TSs cis,anti,endo and trans,anti,exo, deriving from s-cis-1 and s-trans-1, respectively. We have already reported that B3LYP calculations indicate that TSs cis,anti,endo have higher free energies than their cis,anti,exo-6 counter-parts in the performic acid epoxidation of 2-cyclobutenol (by ∼1.6-1.8 kcal/mol)5b and 2-cyclohexenol (by ∼2.0-2.8 kcal/mol)5d both in the gas phase and in solution. In the case of 2-cyclopentenol epoxidation with performic acid, the TS cis,anti,endo is less stable than TS cis,anti,exo-6b by 1.0 kcal/mol (B3LYP/6-31G(d)) and 1.5 kcal/mol (B3LYP/6-311+G(d,p)) both in the gas phase and in solution. As for TSs trans,anti,exo they reside at higher energy than the corresponding TSs trans,anti,endo-7 and tend to transform into TSs cis,anti,endo by rotation of the formate moiety around the breaking O- - -O bond. Thus, the TS trans,anti,exo of the reaction of performic acid with 2-cyclopentenol could be located by using the B3LYP/6-31G(d) method as implemented in TITAN but when this structure was optimized with Gaussian it afforded the TS cis,anti,endo.