· (MW 73.06)
(Diels-Alder dienophile;3 Michael acceptor3)
Physical Data: bp 38-39 °C/80 mmHg.2
Analysis of Reagent Purity: titration against tetraphenylcyclopentadienone.3
Preparative Methods: best prepared by dehydration of 2-nitroethanol using phthalic anhydride (eq 1).2,3 It can also be generated for reactions in situ from several precursors, especially 2-nitroethyl phenyl sulfoxide.4
Handling, Storage, and Precautions: lachrymatory oil. Polymerizes readily in the presence of water and violently with base. Purified compound darkens quickly, but 10% solutions in dry benzene can be kept for 6 months or longer when refrigerated.3
Nitroethylene is a very electron-deficient and highly reactive dienophile in Diels-Alder reactions with electron-rich or unactivated dienes. Its reactions with cyclopentadiene derivatives exhibit particularly high reactivity and selectivity, proceeding at temperatures as low as -100 °C to form only the endo product (eq 2).3,5 Many other cyclic dienes show similar selectivity.6 The adducts are readily converted to ketones, making nitroethylene a useful ketene equivalent.5
Reactions with acyclic dienes proceed much more slowly, and are often carried out at 80-120 °C.7 These reactions exhibit high regioselectivity with simple dienes.8 Subsequent alkylation and denitration (Tri-n-butylstannane) of the adducts (eq 3) effects the overall synthetic equivalent of a regiocontrolled Diels-Alder reaction with 1-alkenes.8
Nitroethylene is also a reactive dipolarophile in 1,3-dipolar cycloadditions.3,9 An interesting observation, rationalizable from FMO considerations, is that the regiochemistry of nitroethylene reactions with nitrones is often reversed from that observed with less electron-deficient alkenes (eq 4).9a,c
Nitroethylene is a reactive and useful acceptor for nucleophilic radicals (eq 5).10
A wide variety of nucleophiles have been used in conjugate additions to nitroethylene.3,11 Avoiding the facile base-mediated polymerization of nitroethylene is crucial to the success of these additions. A broad study found that additions of amines with pK
a values between 2 and 8 are highly successful, while more basic amines lead to polymerization.12 An exception is the pyrrolidine synthesis in eq 6, in which a second Michael addition traps the intermediate nitronate anion.13
Traditional Michael additions of b-dicarbonyl compounds to nitroethylene in protic solvents are best carried out under the most mildly basic conditions possible (KF catalyzed,14 for example).
Kinetic Michael additions of preformed enolates at low temperatures have also been reasonably successful.15
- 1. For a review of nitroalkene chemistry, see: Barrett, A. G. M.; Graboski, G. G. CRV 1986, 86, 751.
- 2. Buckley, G. D.; Scaife, C. W. JCS 1947, 1471.
- 3. Ranganathan, D.; Rao, C. B.; Ranganathan, S.; Mehrotra, A, K.; Iyengar, R. JOC 1980, 45, 1185.
- 4. Ranganathan, S.; Ranganathan, D.; Singh, S. K. TL 1987, 28, 2893. See also ref 11.
- 5. Ranganathan, S.; Ranganathan, D.; Mehrotra, A. K. JACS 1974, 96, 5261.
- 6. (a) Posner, G. H.; Nelson, T. D.; Kinter, C. M.; Johnson, N. JOC 1992, 57, 4083. (b) Van Tamelen, E. E.; Zawacky, S. R. TL 1985, 26, 2833. (c) Corey, E. J.; Myers, A. G. JACS 1985, 107, 5574.
- 7. (a) Ono, N.; Kamimura, A.; Miyake, H.; Hamamoto, I.; Kaji, A. JOC 1985, 50, 3692. (b) Drake, N. L.; Kraekel, C. M. JOC 1961, 26, 41. (c) Kaplan, R. B.; Shechter, H. JOC 1961, 26, 982. (d) Zutterman, F.; Krief, A. JOC 1983, 48, 1135. (e) Ono, N.; Miyake, H.; Kamimura, A.; Tsukui, N.; Kaji, A. TL 1982, 23, 2957.
- 8. Ono, N.; Miyake, H.; Kamimura, A.; Kaji, A. JCS(P1) 1987, 1929.
- 9. (a) Padwa, A.; Fisera, L.; Koehler, K. F.; Rodriguez, A.; Wong, G. S. K. JOC 1984, 49, 276. (b) Sasaki, T.; Eguchi, S.; Yamaguchi, M.; Esaki, T. JOC 1981, 46, 1800. (c) Sims, J.; Houk, K. N. JACS 1973, 95, 5798. (d) Baranski, A.; Cholewka, E. Pol. J. Chem. 1991, 65, 319. (e) Padwa, A.; Goldstein, S. I. CJC 1984, 62, 2506.
- 10. (a) Barton, D. H. R.; Crich, D.; Kretzschmar, G. TL 1984, 25, 1055. (b) Sumi, K.; Di Fabio, R.; Hanessian, S. TL 1992, 33, 749.
- 11. (a) Lambert, A.; Scaife, C. W.; Smith, A. E. W. JCS 1947, 1474. (b) Heath, R. L.; Lambert, A. JCS 1947, 1477. (c) Heath, R. L.; Piggott, H. A. JCS 1947, 1481. (d) Heath, R. L.; Rose, J. D. JCS 1947, 1486. (e) Pelter, A.; Hughes, L. CC 1977, 913. (f) Confalone, P. N.; Lollar, E. D.; Pizzolato, G.; Uskokivic, M. R. JACS 1978, 100, 6291.
- 12. Ranganathan, D.; Ranganathan, S.; Bamezai, S. TL 1982, 23, 2789.
- 13. Barco, A.; Benetti, S.; Casolari, A.; Pollini, G. P.; Spalluto, G. TL 1990, 31, 3039.
- 14. Yanami, T.; Kato, M.; Yoshikoshi, A. CC 1975, 726.
- 15. Curran, D. P.; Jacobs, P. B.; Elliott, R. L.; Kim, B. H. JACS 1987, 109, 5280. Chavdarian, C. G.; Seeman, J. I.; Wooten, J. B. JOC 1983, 48, 492.
Daniel A. Singleton
Texas A&M University, College Station, TX, USA
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