Regiospecific reactions of the ambident anion of bis(pentamethylphenyl)acetonitrile

1992 ◽  
Vol 57 (6) ◽  
pp. 1940-1942 ◽  
Author(s):  
Leo F. Clarke ◽  
Anthony F. Hegarty
Keyword(s):  
Ambident Anion

Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system

1989 ◽  
Vol 67 (4) ◽  
pp. 689-698 ◽  
Author(s):  
Donald R. Arnold ◽  
Shelley A. Mines
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Phenyl Group ◽  
Oxidation Potential ◽  
Original Position ◽  
Acetonitrile Solution ◽  
Steric Interaction ◽  
Ambident Anion

Alkenes, conjugated with a phenyl group, can be converted to nonconjugated tautomers by sensitized (electron transfer) irradiation. For example, irradiation of an acetonitrile solution of the conjugated alkene 1-phenylpropene, the electron accepting photosensitizer 1,4-dicyanobenzene, the cosensitizer biphenyl, and the base 2,4,6-trimethylpyridine gave the nonconjugated tautomer 3-phenylpropene in good yield. Similarly, 2-methyl-1-phenylpropene gave 2-methyl-3-phenylpropene, and 1-phenyl-1-butene gaveE- and Z-1-phenyl-2-butene. The reaction also works well with cyclic alkenes. For example, 1-phenylcyclohexene gave 3-phenylcyclohexene, and 1-(phenylmethylene)cyclohexane gave 1-(phenylmethyl)cyclohexene. The proposed mechanism involves the initial formation of the alkene radical cation and the sensitizer radical anion, induced by irradiation of the sensitizer and mediated by the cosensitizer. Deprotonation of the radical cation assisted by the base gives the ambident radical, which is then reduced to the anion by the sensitizer radical anion. Protonation of the ambident anion at the benzylic position completes the sequence. Reprotonation at the original position is an energy wasting step. Tautomerization is driven toward the isomer with the higher oxidation potential, which is, in the cases studied, the less thermodynamically stable isomer. The regioselectivity of the deprotonation step is dependent upon the conformation of the allylic carbon–hydrogen bond. The tautomerization of 2-methyl- 1-phenylbutene gave both 2-phenylmethyl-1-butène and 2-methyl-1-phenyl-2-butene (E and Z isomers), while 2,3-dimethyl- 1-phenylbutene gave only 3-methyl-2-phenylmethyl-1 -butene. In the latter case, steric interaction of the methyls on the isopropyl group prevents effective overlap of the tertiary carbon–hydrogen bond with the singly occupied molecular orbital, thus inhibiting deprotonation from this site. Keywords: photosensitized, electron transfer, alkene, tautomerization, radical cation.

Regioselectivity control in alkylation reactions of indolyl ambident anion

1990 ◽  
pp. 111 ◽  
Author(s):  
Sadaaki Nunomoto ◽  
Yuhsuke Kawakami ◽  
Yuya Yamashita ◽  
Hisato Takeuchi ◽  
Shoji Eguchi
Keyword(s):  
Ambident Anion ◽  
Alkylation Reactions

Radical ions in photochemistry. 18. The photosensitized (electron transfer) tautomerization of alkenes; the 1,1-diphenyl alkene system

1987 ◽  
Vol 65 (9) ◽  
pp. 2312-2314 ◽  
Author(s):  
Donald R. Arnold ◽  
Shelley A. Mines
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Relative Rate ◽  
Radical Cations ◽  
Radical Ions ◽  
Back Electron Transfer ◽  
Ambident Anion ◽  
Determining Factor

The photosensitized (electron transfer) irradiation of several conjugated 1,1-diphenyl alkenes, in acetonitrile with 1,4-dicyanobenzene or 1-cyanonapthalene as electron accepting sensitizer and 2,6-lutidine as base, leads essentially quantitatively to tautomerization to the less stable unconjugated isomer(s). The proposed mechanism for this reaction involves formation of the alkene radical cation and sensitizer radical anion followed by deprotonation of the radical cation, reduction of the resulting radical to the ambident anion by back electron transfer from the radical anion, and reprotonation. There are several steps in this mechanism that could control the ratio of isomers. Evidence is provided that, at least in some cases, it is the relative rate of deprotonation from the isomeric radical cations that is the determining factor. This rate is influenced by the conformation of the radical cation; the carbon–hydrogen bond involved in the deprotonation step must overlap with the singly occupied molecular orbital.

ChemInform Abstract: 3,5-DIFLUORO-1,3,5-TRIOXO-1Λ6,3Λ6,5Λ6,2,4,6-TRITHIATRIAZIN# -1-OLATE-AN AMBIDENT ANION

1976 ◽  
Vol 7 (22) ◽  
pp. no-no ◽  
Author(s):  
DIEC-LANG WAGNER ◽  
HARTMUT WAGNER ◽  
OSKAR GLEMSER
Keyword(s):  
Ambident Anion

Pyrrole chemistry. XVII. Alkylation of the pyrrolyl ambident anion

1977 ◽  
Vol 55 (23) ◽  
pp. 4112-4116 ◽  
Author(s):  
Nam-Chiang Wang ◽  
Kang-Er Teo ◽  
Hugh J. Anderson
Keyword(s):  
Phase Transfer Catalysis ◽  
Phase Transfer ◽  
Alkyl Halides ◽  
Optimum Conditions ◽  
Alkylation Product ◽  
Ambident Anion ◽  
Series Of Experiments ◽  
C And N ◽  
Substituted Pyrroles

A series of experiments were carried out to find optimum conditions for C- and N-alkylation of the pyrrolyl ambident anion. While almost total C-alkylation could be obtained, isolation of a single alkylation product was not feasible. However, N-alkylation of pyrrole and several 2-substituted pyrroles was readily achieved by phase transfer catalysis with primary alkyl halides.

ChemInform Abstract: PYRROLE CHEMISTRY. XVII. ALKYLATION OF THE PYRROLYL AMBIDENT ANION

1978 ◽  
Vol 9 (13) ◽  
Author(s):  
N.-C. WANG ◽  
K.-E. TEO ◽  
H. J. ANDERSON
Keyword(s):  
Ambident Anion
Sign in / Sign up

Export Citation Format

Share Document