Dichlorodi-m-methoxybis(pyridine)dicopper

[15338-24-6]  · C12H16Cl2Cu2N2O2  · Dichlorodi-m-methoxybis(pyridine)dicopper  · (MW 418.27)

(oxidizing agent for aromatic alcohols;1 useful in preparation of muconic acid monoesters and mononitriles;2 preparation of cyclic orthoesters,3 cyclic imides,2a and lactones1d,2a,4)

Alternate Names: chloromethoxy(pyridine)copper [28733-06-4]; di-m-chlorodimethoxybis(pyridine)dicopper [15094-30-1].

Solubility: modestly sol pyridine; slightly sol methanol, NMP, DMF.

Form Supplied in: green solid.

Preparative Methods: easily prepared by oxidation of Copper(I) Chloride using O2 in methanol/pyridine solution (eq 1).5 There are several other methods for obtaining this reagent, or generating it in situ without isolation (eqs 2-4).5,6

Handling, Storage, and Precautions: the freshly prepared dry solid may be stored briefly at rt and weighed without special precautions. The crystals may be stored indefinitely at rt when sealed under a dry N2 atmosphere to preclude moisture.

Introduction.

The reagent (1) is a selective oxidizing agent for phenol and catechol derivatives, as well as for o-benzoquinones. Pyridine is the preferred solvent. In the solid state (1) exists as methoxy-bridged dimers.7

Oxidative Cleavage of Catechol in the Presence of Water or Oxygen.

Under anaerobic conditions in a pyridine solution of water, methanol, and 3 mol equiv of (1), catechol rapidly undergoes a four-electron oxidative ring opening to cis,cis-muconic acid monomethyl ester at rt (eq 5).1d,3 4-Substituted catechols and o-benzoquinones are also readily cleaved to the corresponding muconic acid ester (eq 6). o-Methoxyphenols are unreactive.

The same cleavage reactions occur in the presence of oxygen. Thus by using different alcohols in the method of eq 2 for generating (1) in situ, monoalkyl and monoaryl esters of muconic acid are available (eq 7).1d Interestingly, phenol undergoes a net six-electron oxidative ring opening only in the presence of oxygen, and at a much slower rate than the other aromatic derivatives already mentioned.

Overall, (1) reacts as a two-electron oxidant, and the suggestion that this oxidant system exemplifies the activation of molecular oxygen1a-c is inconsistent with experimental findings.1d,3,8 Mechanistic studies continue to probe the complex interaction of O2 with similar copper species.9

Oxidations in the Presence of Ammonia.

In the presence of ammonia, (1) oxidizes catechols and o-benzoquinones to a ring-expanded cyclic imide (eq 8).2a Replacing MeOH with ammonia in the method of eq 2 generates a reactive CuII oxidant, related to (1), that cleaves phenols, catechols, and o-benzoquinones to muconic acid mononitriles (eq 9).2,10

Oxidations Under Anaerobic, Anhydrous Conditions.

Under combined anaerobic/anhydrous reaction conditions in pyridine, phenol undergoes no net oxidation in the presence of (1), whereas catechol polymerizes, possibly by forming unstable quinone intermediates. However, 4-t-butylcatechol or 4-t-butyl-6-substituted catechols are subjected overall to a six-electron oxidation, forming a novel cyclic orthoester ester (eq 10).3 Under similar conditions, cyclic anhydrides cleave to a mixture of muconic acid monoester isomers, except in the case of the di-t-butyl anhydride, in which ring opening, lactonization, and chlorination occur (eq 11).4


1. (a) Tsuji, J.; Takayanagi, H. JACS 1974, 96, 7349. (b) Tsuji, J.; Takayanagi, H.; Sakai, I. TL 1975, 1245. (c) Tsuji, J.; Takayanagi, H. TL 1976, 1365. (d) Rogić, M. M.; Demmin, T. R.; Hammond, W. B. JACS 1976, 98, 7441.
2. (a) Demmin, T. R.; Swerdloff, M. D.; Rogić, M. M. JACS 1981, 103, 5795. (b) Demmin, T. R.; Rogić, M. M. JOC 1980, 45, 2737.
3. Demmin, T. R.; Rogić, M. M. JOC 1980, 45, 4210.
4. Demmin, T. R.; Rogić, M. M. JOC 1980, 45, 1153.
5. Finkbeiner, H.; Hay, A. S.; Blanchard, H. S.; Endres, G. F. JOC 1966, 31, 549.
6. Rogić, M. M.; Demmin, T. R. JACS 1978, 100, 5472.
7. Willett, R. D.; Breneman, G. L. IC 1983, 22, 326.
8. Rogić, M. M.; Demmin, T. R. In Aspects of Mechanism and Organometallic Chemistry; Brewster, J. H., Ed.; Plenum: New York, 1978; p 141.
9. (a) Balla, J.; Kiss, T.; Jameson, R. F. IC 1992, 31, 58. (b) Sanyal, I.; Mahroof-Tahir, M.; Nasir, M. S.; Ghosh, P.; Cohen, B. I.; Gultneh, Y.; Cruse, R. W.; Farooq, A.; Karlin, K. D.; Liu, S.; Zubieta, J. IC 1992, 31, 4322.
10. (a) Demmin, T. R.; Rogić, M. M. (Allied Chemical Corporation) U. S. Patent 4 277 419, 1981. (b) Demmin, T. R.; Rogić, M. M. (Allied Corporation) U. S. Patent 4 329 498, 1982 (CA 1982, 97, 128 074x).

Timothy R. Demmin

AlliedSignal, Buffalo, NY, USA



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