Novel tocopheryl compounds. Part 16: Nitration of α-tocopheryl acetate - A mechanistic study

Tetrahedron

Volumn 59, Issue 41, 2003, Pages 8177-8182

  Adelwöhrer, Christian ^a   Rosenau, Thomas ^a   Kosma, Paul ^a  

^a UNIVERSITY OF NATURAL RESOURCES AND LIFE SCIENCES   (Austria)

Author keywords

Nitration; Ortho quinone methide; Reaction mechanism; Tocopheryl acetate; Vitamin E

Indexed keywords

ACETIC ACID DERIVATIVE; ALKYL GROUP; ALPHA TOCOPHEROL; BENZYL DERIVATIVE; NITRIC ACID; NITRITE; TOCOPHERYL; UNCLASSIFIED DRUG;

ARTICLE; CARBON NUCLEAR MAGNETIC RESONANCE; CHEMICAL REACTION; CONCENTRATION (PARAMETERS); MOLECULAR INTERACTION; NITRATION; OXIDATION; PRIORITY JOURNAL; PROTON NUCLEAR MAGNETIC RESONANCE;

EID: 0141682319     PISSN: 00404020     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tet.2003.08.030     Document Type: Article

References (28)

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11. Results will be reported in due course.
12. This reaction gives considerable amounts of the corresponding alkyl nitrite besides the desired products due to the ambifunctionality of nitrite as nucleophile.
13. Formation of 8 from 3 means a formal hydride abstraction from the benzylic position at C-5a. A transfer of two electrons, however, giving a quinoid dicationic intermediate which then releases a proton from C-5a to produce 8, appears more plausible.
14. Ar dihedral angle of 142.4°
15. This spatial arrangement is evidently favored by strong resonance stabilization (66.9 kJ/mol as compared to an acetyl group lying in the aromatic plane, but with the acyl oxygen facing opposite direction, i.e. towards C-7a).
16. The occurrence of similar out-of plane benzylic intermediates derived from α-tocopherol has recently been described and directly observed by NMR: Rosenau T., Potthast A., Elder T., Kosma P. Org. Lett. 4:(24):2002; 4285-4288.
17. 2 group in 5° steps with full geometry optimization in addition to transition state localization. Here, again the crucial role of the acetyl group can be seen. While the value for 8 is high, the rotational barrier shrinks to mere 8.2 kJ/mol in the system without acetyl group.
18. 2 gas. Nevertheless, the positive effect of nitrite addition on the yield was evident.
19. 2 or nitrate by NMMO was negligible, 5 was observed as the major byproduct.
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28. 2 in the presence of TEA (55 mg, 0.50 mmol). After addition of water (100 mL) and extraction with EtOAc 3a was isolated quantitatively. Analytical data are consistent with those given in the literature: Burton G.W., Doba T., Gabe E.J., Hughes L., Lee F.L., Prasad L., Ingold K.U. J. Am. Chem. Soc. 107:1985;7053.