Nucleophilicity of Diazo Compounds
4068 4076
stirred solutions of the benzhydrylium salts in dry CH2Cl2. After fading of
the color, the reaction mixture was stirred with water or NH3, the layers
were separated, and the organic solvent was removed in vacuo. The residue
was purified by crystallization or column chromatography.
On the assumption that the nucleophilicity of dibenzoyl-
diazomethane resembles that of diethyl diazomalonate (1g),
Figure 3 explains why this compound does not even react with
the p-nitrobenzenediazonium ion (21a).[39] Since the 2,4-
dichlorobenzenediazonium ion can be expected to have an
electrophilicity parameter similar to that of the p-nitro-
benzenediazonium ion (based on Hammett×s s), its reported
azo coupling with diazoacetone[39] is also in agreement with
Figure 3.
For details and characterization of the products see the Supporting
Information.
Concentrations and rate constants for the individual kinetic experiments
for the reactions of diazo compounds with benzhydryl cations are given in
the Supporting Information.
The higher nucleophilicity of diphenyldiazomethane (1d)
than of ethyl diazoacetate (1e)is in agreement with the report
that the benzenediazonium ions 21a c react with 1d within a
Acknowledgement
We thank Professor R. Huisgen for valuable comments and suggestions and
Roland Weisser for performing kinetic experiments with 1c and 1d.
Financial support by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie is gratefully acknowledged.
few minutes to give the a-phenylazobenzhydryl ethers 23a
c
in 54 70% yield[39] (Scheme 14).
[1] R. Huisgen in 1,3-Dipolar Cycloaddition Chemistry, (Ed.: A. Padwa),
J. Wiley, New York, 1984, pp. 1 31.
[2] a)M. Regitz, Diazoalkane: Eigenschaften und Synthesen, Thieme,
Stuttgart, 1977; b)H. Zollinger, Diazo Chemistry I, VCH, Weinheim,
1994; c)H. Zollinger, Diazo Chemistry II, VCH, Weinheim, 1995;
d)T. Ye, M. A. McKervey, Chem. Rev. 1994, 94, 1091 1160.
[3] J. Fink, M. Regitz, Synthesis 1985, 569 585.
Scheme 14. Reactions of the diazonium ions 21a c with diphenyldiazo-
methane (1d).[39]
[4] R. Huisgen, Angew. Chem. 1955, 67, 439 461.
[5] a)A. Ledwith, Y. Shih-Lin, J. Chem. Soc. B 1967, 83 84; b) R.
Huisgen, Angew. Chem. 1963, 75, 742 754; Angew. Chem. Int. Ed.
Engl. 1963, 2, 633 645; c)R. Huisgen, Angew. Chem. 1963, 75, 604
637; Angew. Chem. Int. Ed. Engl. 1963, 2, 565 598.
[6] W. Bihlmaier, R. Huisgen, H.-U. Reissig, S. Voss, Tetrahedron Lett.
1979, 2621 2624.
[7] K. Fukui, Angew. Chem. 1982, 94, 852 861; Angew. Chem. Int. Ed.
Engl. 1982, 21, 801 809.
[8] K. N. Houk in Pericyclic Reactions, (Eds.: A. P. Marchand, R. E.
Lehr), Vol. 2, Academic Press, 1977, pp. 181 271.
[9] a)H. Mayr, M. Patz, Angew. Chem. 1994, 106, 990 1010; Angew.
Chem. Int. Ed. Engl. 1994, 33, 938 957; b)H. Mayr, B. Kempf, A. R.
Ofial, Acc. Chem. Res. 2003, 36, 66 77.
[10] a)M. Hartnagel, K. Grimm, H. Mayr, Liebigs Ann. 1997, 71 80; b)H.
Mayr, J. Henninger, Eur. J. Org. Chem. 1998, 1919 1922; c)H. Mayr,
A. R. Ofial, J. Sauer, B. Schmied, Eur. J. Org. Chem. 2000, 2013 2020;
d)C. Fichtner, H. Mayr, J. Chem. Soc. Perkin Trans. 2 2002, 1441
1444.
As predicted by Figure 3, the p-nitrobenzenediazonium ion
(21a)reacts rapidly with phenyldiazomethane ( 1b), but as in
reactions with tritylium and benzhydrylium ions, identifica-
tion of the products was not possible.[39]
The highly nucleophilic diazomethane (1a)(see Figure 3)
was found to react both with p-nitro- and with the unsub-
stituted benzenediazonium ion.[39] Since product studies
indicated a different type of mechanism in these reactions
([32] cycloadditions), application of Equation (1) is not
possible. In future work, the rates of 1,3-dipolar cycloaddition
reactions will be compared with the rates predicted by
Equation (1), in order to gain further insight in the mecha-
nisms of these reactions.
[11] H. Mayr, T. Bug, M. F. Gotta, N. Hering, B. Irrgang, B. Janker, B.
Kempf, R. Loos, A. R. Ofial, G. Remennikov, H. Schimmel, J. Am.
Chem. Soc. 2001, 123, 9500 9512.
[12] a)R. Lucius, H. Mayr, Angew. Chem. 2000, 112, 2086 2089; Angew.
Chem. Int. Ed. 2000, 39, 1995 1997; b)R. Lucius, R. Loos, H. Mayr,
Angew. Chem. 2002, 114, 97 102; Angew. Chem. Int. Ed. 2002, 41,
91 95.
[13] a)H. Mayr, G. Lang, A. R. Ofial, J. Am. Chem. Soc. 2002, 124, 4076
4083; b)S. Minegishi, H. Mayr, J. Am. Chem. Soc. 2003, 125, 286 295.
[14] Though the following discussion considers diazonium ions as inter-
mediates, our results are also in accord with mechanisms in which
Experimental Section
The benzhydryl salts Ar2CH (see Table 1)were prepared as described. [11]
(Trimethylsilyl)diazomethane (1c, 2m in hexane)and ethyl diazoacetate
(1e, ꢂ10% in CH2Cl2)were purchased from Fluka. Diazomethane ( 1a)
was prepared from N-methyl-N-nitroso-p-toluenesulfonamide with KOH
in CH2Cl2/n-butanol instead of by using ether and ethanol as solvents as
described.[40] The reaction flask was kept at 608C and diazomethane
distilled off immediately after formation. For the preparative investiga-
tions, diazomethane was distilled directly into the solution of the
benzhydrylium salts through a condenser, which keeps back the refluxing
solvent. For the kinetic experiments, 1a was used as a solution in CH2Cl2.
The concentrations of the solutions of 1a, 1c, and 1e were determined
directly before use by titration as described.[41]
À
cleavage of the C N2 bond starts before the electrophilic addition is
complete. Quantum chemical calculations indicate that the benzyl-
diazonium ion does not exist: a)R. Glaser, C. J. Horan, E. D. Nelson,
M. K. Hall, J. Org. Chem. 1992, 57, 215 228; b)R. Glaser, D. Farmer,
Chem. Eur. J. 1997, 3, 1244 1253.
[15] a)H. Meerwein, Angew. Chem. 1948, 60, 78; b)S. W. Kantor, R. C.
Osthoff, J. Am. Chem. Soc. 1953, 75, 931 932.
Phenyldiazomethane (1b)[42] (from benzaldehyde p-toluenesulfonylhydra-
¬
[16] a)J.-F. Le tard, R. Lapouyade, W. Rettig, Chem. Phys. Lett. 1994, 222,
zone[42])diphenyldiazomethane
(
1d)[43] (from commercially available
209 216; b)M. Singh, K. N. Singh, R. A. Misra, Ind. J. Chem. 1994,
33B, 173 176; c)W. Tadros, L. Ekladius, A. B. Sakla, J. Chem. Soc.
1954, 2351 2353; d)F. H. C. Stewart, J. Org. Chem. 1961, 26, 3604
3605.
benzhydrylidene hydrazine), diazoacetone (1 f)[44] (from acetyl chloride
and diazomethane), and diethyl diazomalonate (1g)[45] (from diethyl
malonate and tosyl azide[46])were prepared as described in the literature.
Products of the reactions of the diazo compounds 1 with the benzhydrylium
[17] G. R. Newkome, J. M. Robinson, J. Org. Chem. 1976, 41, 2536 2540
[18] R. Rossi, A. Carpita, P. Cossi, Tetrahedron 1992, 48, 8801 8824.
salts Ar2CH XÀ were synthesized by addition of the diazo compounds to
Chem. Eur. J. 2003, 9, 4068 4076
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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