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Photocatalyzed Multiple Additions of Amines to a,@-Unsaturated Esters and Nitriles’ Suresh Das,**2aJ, S. Dileep Kumar,” K. George Thomas,% K. Shivaramayya,%and M. V. George+,2apb Photochemistry Research Unit, Regional Research Laboratory (CSIR), Trivandrum 695 019, India, and Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556 Received August 6, 1993.
Photoelectron-transfer-catalyzedintermolecular carbon-carbon bond formation of primary, secondary, and tertiary amines with a,@-unsaturated esters and nitriles using photosensitizers such as anthraquinone, acridone, and dicyanoanthracene has been investigated. The addition of a-aminoalkyl radicals, generated via photoelectron-transfer processes, to olefinic substrates and the subsequent 1,5-hydrogenabstraction reactions of the amine-olefin adduct radicals lead to a number of interesting multiple-olefii-added products. The adducts of the primary and secondary amines with a,@unsaturated esters undergo further cyclizations to give spiro and cyclic lactams, respectively.
Introduction The generation and subsequent reactions of a-aminoalkyl radicals have been topics of extensive studies in recent Such radicals can be utilized for the construction of carbon-carbon bonds adjacent to nitrogen, which is of significant importance in alkaloid chemistry.12-14 There have been numerous studies on the mechanistic and synthetic aspects of additions of amines to alkenes, initiated by the direct excitation of the alkenes.s4 More recently, the intra- and intermolecular carbon-carbon bond forming reactions of a-aminoalkyl radicals, generated via photosensitized electron-transfer reactions of a-silylamines, using sensitizers such as dicyanoanthracene (DCA) and dicyanonaphthalene (DCN), have been investigated.337J4Following the formation of the alkylamino radical cation in the initial electron transfer process, the loss of the a-silyl group facilitates the generation of a-aminoalkyl radicals in good yields. Although there are several reports on the mechanistic aspects of a-aminoalkyl radical generation from amines, using a variety of sensitizer systems such as ketones, flavins, porphyrins, and semiconductors,lOJlthere have been only a few attempts to utilize these processes for carbon-carbon bond forming reactions. Electron-transfer reactions between excited state ketones and ground-state amines have + Also at the Jawaharlal NehruCentre for Advanced Scientific Research, Bangalore 560 012, India. Abstract published in Advance ACS Abstracts, December 15,1993. (1) Contribution No. RRLT-PRU-34 from the Regional Research Laboratory, Trivandrum and No. NDRL-3629from the Notre Dame Radiation Laboratory. (2) (a) Regional Research Laboratory, Trivandrum. (b) University of Notre Dame: (3) Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 1992,25, 233. (4) Lewis, F.D. Acc. Chem. Res. 1986, 19, 401. (5) Bermark, W. R.; DeWan, C.; Whitten, D.G. J. Am. Chen. SOC. 1992,114,-8810. (6) Lewis, F.D.; Ho, T.-I.; Simpson, J. T. J. Org. Chem. 1981,46,1077. (7) Yoon,U.C.;Kim,Y.C.;Choi, J. J.;Kim,D.U.;Mariano,P. S.;Cho, 1.-S.; Jeon, Y. T. J. Org. Chem. 1992,57, 1422. (8) Pandey, G.; Kumarasamy, G. Tetrahedron Lett. 1988, 4153. (9) Giese, B. Radicals in Oraanic Synthesis: Formation of CarbonCarbon Bonds; Pergamon Preis: New York, 1986. (10) Pienta, N. J. In Photoinduced Electron Transfer; Fox, M. A., Chanon, M., Eds.; Elsevier: Amsterdam, 1988; Part C. (11) Ci, X.; Whitten, D. G. In Photoinduced Electron Transfer; Fox M. A., Chanon, M., Eds.; Elsevier: Amsterdam, 1988; Part C. (12) Hart, D. J.; Tsai, Y.-M. J. Am. Chem. SOC.1982,104,1430. (13) Jung, Y. S.; Mariano, P. S. Tetrahedron Lett. 1993, 34, 4611. (14) Pandey, G.; Reddy, G. D. Tetrahedron Lett. 1992,33,6533.
been extensively ~tudied.~~J~Jf+19 Picosecond laser flash photolysis studies have shown that the mechanism of electron transfer in acetonitrile solutions involves the formation of a triplet exciplex which changes to a contact ion-pair. The contact ion-pair decays via intramolecular proton transfer within the picosecond time domain. The intramolecular proton transfer is facilitated by the strongly basic nature of the ketyl radical a n i ~ and n ~the ~ acidic ~ ~ nature of the alkylamine radical cation.21 Thus, even with a-silylamine-enone systems, direct excitation of enones in aprotic solvents leads to the deprotonated a-aminoalkyl radical in preference to the desilylated aminoalkyl r a d i ~ a l . ~ Here we report on our studies on the photosensitized generation and subsequent intermolecular carbon-carbon bond forming reactions of a-aminoalkyl radicals from underivatized amines using anthraquinone and acridone as sensitizers and have compared these to the reactions sensitized by DCA. The addition of primary, secondary, and tertiary amines to a few a,p-unsaturated esters and nitriles has been investigated. Both anthraquinone and acridone will generate ketyl radicals, following the initial electron-transfer process, and based on the above discussions, would be expected to generate a-aminoalkyl radicals from underivatized amines more efficiently than DCA.
Results Photosensitized Addition Reactions of Triethylamine (2) with Methyl Methacrylate (5) and Acrylonitrile (18). The photosensitized addition of triethylamine (2) to methyl methacrylate (5) was effected by (15) (a) Simon, J. C.; Peters, K. S., J.Am. Chem. SOC.1981,103,6408. (b)Manning, L. E.; Peters, K. S. J.Am. Chem. SOC.1985,107,6452. (c) Simon,J. D.;Peters, K. S. J.Am. Chem.SOC.1983,105,4875. (d) Schaefer, C. G.; Peters, K. S. J. Am. Chem. SOC.1980,102, 7566. (16) Cohen, S. G.; Baumgarten, R. J. J.Am. Chem. Soc. 1966,87,2996. (17) Inbar, S.;Linschitz, H.; Cohen, S. G. J.Am. Chem. SOC.1981,103, 1048.
(18) (a) Nakayama, T.; Uahida, K.; Hamanoue, K. J. Chem. SOC. Faraday Trans.1990,86,95. (b) Hamanoue, K.; Nakayama, T.; Sugiura, K.; Teranishi, H.; Washio, M.; Tagawa, S.; Tabata, Y. Chem. Phys. Lett. 1986,118,503. (c) Hamanoue, K.; Sawada, K.; Yokoyama, K.; Nakayama, T.; Hirase, S.; Teranishi, H. J.Photochem. 1986, 33, 99. (19) Bhattacharyya, K.; Das, P. K. J. Phys. Chem. 1986,90,3987. (20) Hayon, E.; Ibata, J.; Lichtin, N. N.; Simic, M. J. Phys. Chem.
1972, 76,2072. (21) Daa, S.; von Sonntag, C. Z. Naturforsch. 1986, 41b, 505. (22) Dinnocenzo, J. P.; Banach, T. E. J. Am. Chem. SOC.1989,111, 8646.
0022-3263/94/1959-0628$04.5QlQ 0 1994 American Chemical Society
J. Org. Chem., Vol. 59,No. 3, 1994 629
Photocatalyzed Multiple Additions
Scheme 1
Table 1. Photosensitized Addition of Triethylamine (2) to Methyl Methacrylate (5) in Acetonitrile (350 mL) at 290 Ha sensitizer (30-40 pM) anthraquinone anthraquinone anthraquinone anthraquinone anthraquinone anthraquinone anthraquinone acridone acridone dicyanoanthracene dicyanoanthracene a Irradiation
2 (“01)
15 15 15 15 15 15 lo00 15 15 15 15
5 (mmol)
time of irradiation (h)
% conversion of 5
15 15 15 15 2 45 15 15 15 15 15
1 2 3 4 1 1 1 1 4 4 8
20 26 30 40 42 17 20 28 38 8 12
8
10 10 10 10 8 10 20 10 10
35 30
product distribution (%)* 11 12 20 18 15 14 18 14 25 20 18 22 24
28 28 25 24 26 24 30 32 30 18 20
17
12 16 18 22 8 15 10 18 20 5 8
by Pyrex-filtered light of a 450-W medium pressure Hanovia Lamp. b Yield based on conversion of 5.
irradiating argon-saturated acetonitrile solutions of triethylamine and methyl methacrylate containing catalytic amounts of anthraquinone (l),under Pyrex-filtered light (A > 290 nm). Four products were isolated from the reaction mixture (8,11,12,17, Scheme 1)and they were characterized on the basis of spectral information. The yields and percentage conversion and distribution of products under a variety of irradiation conditions are shown in Table 1. Change of irradiation time as well as
substrate concentration brought about only minor changes in the product distribution. On use of large excess of triethylamine (0.15-1mol) there was some increase in the yield of 8 a t the expense of 17. On using acridone as sensitizer, instead of anthraquinone, the percentage conversion and product yields were comparable (Table 1). Dicyanoanthracene however was observed to be much less efficient as sensitizer when compared to anthraquinone and acridone (Table 1). Also, the percentage distribution
630 J. Org. Chem., Vol. 59, No.3, 1994
Das et al.
Scheme 2
(CH&H&N
2
+
CHzzCH-CN
-
-CN
NC,
-CN
1,hv
CH3CN
f.jCN
1I1
4
CN CN
CN
a
19
+
ky CN
/
2Q
CN
CN CN
Table 2. Photosensitized Addition of Triethylamine (2) to Acrylonitrile (18) in Acetonitrile (350 mL)at 290 E(. 2 18 time of % product distribution (%)* sensitizer (1o-L M) (mmol) (mmol) irradiation (h) conversion of 18 19 20 21 + 22 anthraquinone 15 15 1 17 8 10 60 anthraquinone 15 45 1 11 8 12 50 150 15 1 21 10 15 40 anthraquinone 1 30 18 42 28 15 15 acridone dicyanoanthracene 15 15 1
