Organometallics 1995, 14, 3712-3716
3712
Tetramethylammonium Pentacarbonyl[1-oxidoalkylidene]chromate(0)Salts as Acyl Anion Synthons in Michael Addition Reactions Bjorn C. Soderberg,*J Danny C. York, Elizabeth A. Harriston, H. John Caprara, and Ashley H. Flurry Departments of Chemistry, West Virginia University, P.O. Box 6045, Morgantown, West Virginia 26506-6045, and University of South Alabama, Mobile, Alabama 36688 Received March 23, 1995@ Thermal and photolytic reactions of tetramethylammonium pentacarbonyl[ l-oxidoalkylidenelchromate(0) salts with various electron-deficient alkenes have been investigated. Reaction of these electron-rich carbene complexes with 3-buten-2-one and methyl acrylate compounds, formal Michael addition products derivatives affords 1,4-dicarbonyl-substituted of a n acyl anion and the alkene, in fair to good yield.
Introduction One of the very first synthetically useful reactions of alkoxy-substituted Fischer carbene complexes is the 11 cycloaddition reaction with electronformal [2 deficient alkenes providing functionalized donoracceptor (“push-pull”) substituted cyclopropanes as the major p r o d u ~ t . ~Related ,~ cyclopropanation reactions have also been reported employing electron-rich alkenes such as enol ethers although under substantially different reaction ~onditions.~ In addition to cycloaddition products, minor amounts of acyclic compounds derived from insertion into the P-CH bond of the alkene or by acid-catalyzed cleavage of the cyclopropane ring have been isolated in a few cases. For example, thermal reaction of pentacarbonyl[l-methoxyethylidenelchromium(0) (1)with methyl acrylate in 1,2-dichloroethane gave a 1:l:lratio of the cyclopropane 2, the P-CH insertion product 3,and methyl 4-oxopentanoate (4) in 72% yield (Scheme 1).2c In contrast to the cyclopropanation reactions of “neutral” Fischer carbene complexes, we have recently observed that the electron-rich tetramethylammonium pentacarbonyl[l-oxidoethylidenelchromate(0)complex 5a can be used as an acyl anion synthon. It was shown that formal Michael addition adducts are formed from reactions of 5a with a number of a,P-unsaturated ketones and ester^.^^^ For example, irradiation of a 0.1
+
@Abstractpublished in Advance ACS Abstracts, July 1, 1995. (1)Address all correspondence to West Virginia University. (2)For examples, see: (a) Wienand, A,; Reissig, H.-U. Chem. Ber. 1991,124,957.(b) Herndon, J. W.; Tumer, S. U. J . Org. Chem. 1991, 56,286.(c)Wienand, A.; Reissig, H.-U. Organometallics 1990,9,3133. (d) Wienand, A.; Reissig, H.-U. Tetrahedron Lett. 1988,29,2315. (e) Buchert, M.;Reissig, H.-U. Tetrahedron Lett. 1988, 29, 2319. (0 Dorrer, B.; Fischer, H.; Kalbfus, W. J . Organomet. Chem. 1974,81,C 20. (g) Cooke, M. D.; Fischer, E. 0. J . Organomet. Chem. 1973,56, 279. (h) Dotz, K.H.; Fischer, E. 0. Chem. Ber. 1972,105,1356. (i) 0) Fischer, E. Fischer, E.0.;Dotz, K. H. Chem. Ber. 1970,103,3966. 0.;Dotz, K. H. Chem. Ber. 1970,103,1273. (3)For a review on donor-acceptor-substituted cyclopropanes, see: Reissig, H.-U. Top. Curr. Chem. 1988,144,73. (4) Dotz, K. H.; Fischer, E. 0. Chem. Ber. 1972,105,3966. For a review on more recent work, see: Brookhart, M.; Studabaker, W. B. Chem. Rev. 1987,87, 411. (5)(a) Soderberg, B. C.; York, D. C.; Hoye, T. R.; Rehberg, G. M.; Suriano, J. A. Organometallics 1994,13,4501. (b) Presented in part by B.C.S. at the 205th ACS National Meeting, Denver, CO, 1993.
Scheme 1
1
2 Me0 MeLC02Me
+
MeLC02Me
3
4
Scheme 2
M e%
CO2M e
+
Cr(C0)6
6
M tetrahydrofuran solution of 5 a in the presence of methyl crotonate produced methyl 3-methyl-4-oxo-pentanoate (6)in 57%yield (Scheme 2). Although the yield of 6 was unchanged when the reaction was performed under a carbon monoxide atmosphere (6atm), a significant amount of chromium hexacarbonyl can be isolated and recycled for the preparation of Sa. Some aminosubstituted chromium carbenes also afford formal Michael addition adducts upon reaction with electron deficient alkenes.2c For example, reaction of the dimethylamino-substituted complex 7 with methyl acrylate gave methyl 4-oxopentanoate (4) in excellent yield (Scheme 3).7 A number of mechanistic formalisms can be entertained for the formation of 6,and related 1,4(6)For reactions of other metal acylates with Michael acceptors forming 1,Caddition products, see the following. For nickel: (a) Corey, E. J.; Hegedus, L. S. J . Am. Chem. SOC.1969,91,4926. (b) Semmelhack, M. F.; Keller, L.; Sato, T.; Spiess, E. J . Org. Chem. 1982,47, 4382. (c) Hermanson, J. R.; Gunther, M. L.; Belletire, J. L.; Pinhas, A. R. J . Org. Chem. 1996,60, 1900. For manganese: Hoye, T. R.; Rehberg, G. M. Organometallics lgeO,9,3014. For cobalt: Hegedus, L. S.; Perry, R. J. J . Org. Chem. 1986,50, 4955. (7)Sierra, M. A,; Soderberg, B. C.; Lander, P. A.; Hegedus, L. S. Organometallics 1993,12,3769.
0276-733319512314-3712$09.00/0 0 1995 American Chemical Society
Organometallics, Vol.14, No.8, 1995 3713
Pentacarbonyl[l-oxidoa2kylidene]chromate(0)Salts
Table 1. Reaction of Tetramethylammonium Pentacarbonyl[1-oxidoalkylidene]chromate(O) Complexes with 3-Buten-2-oneunder Thermal and Photochemical Conditions
Scheme 3 (C0)5Cr--/
NMe2
&CO2Me,
MeLCOIMB
Me
7
Entry
Carbenea
Conditions,timeb
4
dicarbonyl products discussed below, but at the present time these are only speculative.8 Several organic synthons are available for the introduction of acyl groups, but they all require an additional deprotection step.g It is conceivable that the easily prepared, highly crystalline tetramethylammonium pentacarbonyl[l-oxidoalkylidenelchromate(0)salts employing mild reaction conditions may offer some advantages over the presently available acyl synthons. Herein we report a more general study of the reaction of a number of alkyl- and aryl-substituted tetramethylammonium salts with pentacarbonyl[ 1-oxidoalkylidenelchromate(0~ 3-buten-2-one and methyl acrylate derivatives.
Results and Discussion A selected number of isolated tetramethylammonium pentacarbonyl[1-oxidoalkylidenelchromate(0)complexes were reacted with 3-buten-2-one. Both alkyl- and arylsubstituted complexes, prepared by addition of the appropriate organolithium reagent to chromium hexacarbonyl followed by exchange of the countercation from lithium to tetramethylammonium, were examined. The reactions were performed in tetrahydrofuran under both photochemical conditions using a 450-W ConradHanovia 7825 medium-pressure mercury lamp equipped with a Pyrex well as well as under thermal conditions at 75 "C (oil bath temperature). The results of these experiments are summarized in Table 1. A 1 to -1.1 ratio of chromium complex to 3-buten-2-one was used for entries 1-3 and 5-15 (Table 1) producing in all instances only minute amounts (
