Maroulis, Shigemitsu, Arnold
/
535
Photosensitized Cyanation of Olefins
and of a simple formula for the metal-hydroperoxide complex has been adopted for simplicity. It is recognized that the metal exists in a m e highly coordinated state. This paper does produce evidence, however, that the hydroperoxide complexes with the metal in a 1:l ratio. (16)C. Walling, "Free Radicals in Solution", Wiley, New York, N.Y., 1957, Chapter 9. (17) F. R. Mayo, Acc. Chem. Res., 1, 193 (1988). (18)K. U. Ingold, Acc. Chem. Res., 2, l(1969). (19)G.Scott, "Atmospheric Oxidation and Antioxidants", American Elsevier, New York, N.Y., 1965. (20) M. S.Kharasch, A. Fono, W. Nudenberg. and B. Bischof, J. Org. Chem., 17. 207 119521. (21) M . ~ SKharaGh, . P. Pauson, and W. Nudenberg, J. Org. Chem., 18, 322
(36)J. A. Howard and K. U. Ingold, Can. J. Chem., 47, 3797 (1969). (37)C. Hansen and A. Beerbower, "Encyclopedia of Chemical Technology", Supplement Volume, 2nd ed, Wliey, New York, N.Y., 1971, pp 889910. (38)F. Haber and J. Weiss, Proc. R. SOC.London, Ser. A, 147, 332 (1934). (39)C. Walling, J. Am. Chem. SOC., 91, 7590 (1969). (40)J. K. Kochi and R. V. Subramanian, J. Am. Chem. SOC., 87, 4855 (1965). (41) A referee has pointed out that reaction 1 1 can be written as ROp 4- CO"
--* R 0 2 -
4- Co3+
(18)
(1953). (22) P. George and A. Robertson, Trans.FaradaySoc., 42, 217 (1946). (23) B. G.Freiden, Zh. Prikl. Khim., 30,788 (1957). (24)J. K. Kochi, Tetrahedron, 18, 483 (1962). (25)J. K. Kochi, J. Am. Chem. SOC.,85, 1958 (1963). (26)J. K. Kochi and H. E. Mains, J. Org. Chem., 30, 1862 (1965). (27)C. Walling, Acc. Chem. Res., 8, 125 (1975). (28)J. A. Howard, Adv. Free-Radical Chem., 4, 49-173 (1972)(Table 18). (29)W. H. Richardson, J. Am. Chem. SOC., 87, 247, 1096 (1965). (30)W. H. Richardson, J. Am. Chem. SOC.,88, 975 (1966). (31) K. Kagami, Bull. Chem. Soc. Jpn., 41, 1552 (1968). (32)N. Laurendeau and R. F. Sawyer, "General Reaction Rate Problems: Combined Integration and Steady State Analysis", Report No. TS-70-14,
which implies that only the addition of a proton is needed to result in the generation of a complex which can produce initiation through reaction 6. Evidence against the validity of this implication is the fact that the lower arid Mn11.23are experimentally observed to produce valence ions of cO'~3~22 true inhibition. To do so they must react to remove one of the radicals responsible for chain propagation by a reaction which cannot result in the initiation of another chain. Emanuel et aLi4 postulate the production of a ketone as a noninitlator product from reaction 18.TkBE et ai.43 postulate the production of a very stable, Ion lived radical complex which does not convert to a hydroperoxide. Ingold4.Fcites evidence against this conclusion. In any case, as mentioned before, the experimental evidence for inhibition indicates that the radical scavenging action of Co2+ and Mn2+ ions does not regenerate a chain initiator. (42)Y. Kamiya, S.Beaton, A. Lafortune, and K. U. Ingold, Can. J. Chem., 41,
Thermal Systems Division, Department of Mechanical Engineering, University of California, Berkeley. (33)D. G.Hendry, T. Mill, L. Piszkiewicz, J. A. Howard, and H. K. Eigenmann, J. Phys. Chem. Ref. Data, 3, 971 (1974). (34)P. Wagner and C. Walling, J. Am. Chem. SOC.,87, 5179 (1965). (35)E. M. Tochina, L. M. Postnikov, and V. Ya. Shlyapintokh, lzv. Akad. Nauk SSSR, Ser. Khim., 71 (1968).
2020 (1963). (43) A. TkBE, K. Vesely, and L. Omelka, J. Phys. Chem., 75, 2575 (1971). (44)K. U. Ingold, J. Phys. Chem., 78, 1385 (1972). (45)V. H. Gol'dberg and L. K. Obukhova, Dok. Akad. Nauk SSSR, 185, 860 (1965). (48)E. T. Denisov and N. M. Emanuel, RUSS. Chem. Rev. ( h g l . Trans/.), 29,645 (1960).
Radical Ions in Photochemistry. 5. Photosensitized (Electron Transfer) Cyanation of Olefins' A. J. Maroulis, Y. Shigemitsu,* and D. R. Arnold* Contribution from the Photochemistry Unit, Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7, Canada. Received February 9, 1977
Abstract: The ultraviolet irradiation of phenyl olefins (1,l-diphenylethylene (Ia), 2-phenylnorbornene (Ib), and l-phenylcyclohexene (IC)) and potassium cyanide in acetonitrile-2,2,2-trifluoroethanolsolution, in the presence of 1-cyanonaphthalene (11) or methyl p-cyanobenzoate (111) photosensitizer (electron transfer), gives good yields of nitriles having the anti-Markownikoff orientation. The reaction is believed to involve electron transfer from the olefin (Ia-c) to the singlet excited state of the sensitizer (I1 or 111) and subsequent reaction of the radical cation of the olefin. Fluorescence quenching studies (the olefins of I1 and 111, and (Ia-c) quench the fluorescence emission of 11) and thermodynamic considerations (El/2°Xof Ia-c, singlet energies) are consistent with the proposed mechanism.
Introduction We have shown, in previous parts of this series, that the photosensitized (electron transfer) addition of oxygen-centered nucleophiles to olefins can be a synthetically useful reaction for the preparation of alcohols, ethers, and esters having the anti-Markownikoff ~ r i e n t a t i o n The . ~ utility of this type of reaction has now been extended to include carbon-carbon bond formation; we have found conditions where cyanide ion can serve as the nucleophile. There are many photochemically induced nucleophilic aromatic substitution reaction^.^ Several of these examples involve substitution with cyanide ion. However, the examples of photoaddition of nucleophiles to aromatic hydrocarbons5 are rare and this report describes the first examples of the addition of cyanide ion to olefins. We found that when 1,l-diphenylethylene (Ia), 2-phenylnorbornene (Ib), or 1-phenylcyclohexene (IC), in acetonitrile-2,2,2-trifluoroethanol solution, was irradiated in the presence of 1-cyanonaphthalene (11) or methyl p-cyanoben0002-7863/78/1500-0535$01.00/0
zoate (111), (electron acceptor sensitizer), and potassium cyanide (reactions 1,2, and 4),good yields (between 40 and 50%) of the nitriles having the anti-Markownikoff orientation (IV, VI, VIII, XII, and XIV) were obtained. Products having the Markownikoff orientation were not detected. Ethers resulting from the anti-Markownikoff addition of the 2,2,2-trifluoroethanol, present as a nonnucleophilic proton source in the reaction mixture, were sometimes formed in small yield (50%) recovered. The progress of the reaction was followed by nuclear magnetic resonance spectroscopy (NMR) and/or by vapor phase chromatography (VPC). The products were isolated from the reaction mixture by column chromatography and were further purified by preparative VPC. Details are given in the Experimental Section. The structure of the products of reaction 1 rests on direct comparison of their infrared (IR) spectra with those of authentic samples. The structures and the stereochemistry assigned to the products from reaction 2 were based on an analysis of the N M R spectrum, in conjunction with the corresponding deuterated products from reaction 3, and were confirmed by independent synthesis as outlined in Scheme 11.
Maroulis, Shigemitsu, Arnold
/ Photosensitized Cyanation of Olefins
Scheme 11
Table I. Fluorescence Quenching of 1-Cyanonaphthalene (11) by 1,I-Diphenylethylene (Ia), 2-Phenylnorbornene (Ib), and 1Phenvlcvclohexene (IC) in Acetonitrile Solution at 20 OC FluoroDhor
I
C&
537
T.
ns
1-Cyanonaphth- 8.92" alene
\
H
XVII
1
HNNH
XVIII
1
HNNH
Ia
kq, M-l Ib
s-l
1.26 X 1Olo 4.80 X 10'O
IC 1.43 X 1O'O
Exciting the fluorophor at 313 nm. We a Taken from ref 3c. consider this value an indication of the magnitude of kq rather than an accurate value, since rapid polymerization and colloid formation occurred after distillation of the purified sample (Ib). Table 11. Half- Wave Oxidation and Reduction Potentials Obtained by Cyclic Voltammetrya
H
Compd
XIX
1-Cyanonaphthalene (11) Methyl p-cyanobenzoate (111) 1,l-Diphenylethylene(Ia) 2-Phenylnorbornene (Ib) 1-Phenylcyclohexene (IC)
t B' H VI1
The triplet signal at 6 3.52 of VI indicated the presence of one exo proton. Irradiation of a solution of 2-phenylnorbornene (Ib) in methanol-0-d and acetonitrile, in the presence of I1 and potassium cyanide (reaction 3), afforded X, which is the corresponding monodeuterated nitrile of VI, and XI, which is the monodeuterated nitrile of VII. (In addition to these products, XI1 was obtained and identified by comparison with an authentic sample.3b)The N M R spectrum of X showed complete loss of the triplet at 6 3.52, which indicates that this triplet is due to H3. Therefore, the structure of VI was assigned as 2exo-cyano-3-endo- phenylnorbornane. The N M R spectrum of VI1 displayed a typical ABX multiplet at 6 3.01. This multiplet collapsed to a doublet pair ( J 2 , 3 = 9 H z ) ~while H7a was irradiated (6 around 1.53). This indicates that both H2 and H3 are coupled to H7a through long-range interaction and is consistent with these two protons being in the endo position. The signal assignment for H2 and H3 was consistent with an analysis of the NMR spectrum of the deuterated nitrile XI, which showed a broad singlet at 6 3.0 attributable to H2 coupled to H7a. This indicates that H2 is not significantly coupled to H I and therefore must be in the endo position. The structure assigned then to VI1 was 2-exocyano-3-exo- phenylnorbornane. The presence of a double bond in the minor product VI11 was verified by a weak absorption band in the IR spectrum at 1570 cm-I .8 The mass spectrum of VI11 showed a peak assigned to the parent ion. The N M R spectrum showed no olefinic hydrogens. Therefore, the structure tentatively assigned for VI11 was 2-cyano-3-phenylnorbornene-2. The structures assigned to VI and VI1 were confirmed by the alternative synthesis outlined in Scheme 11. The spectra (mass, IR, NMR) of the intermediates XVII, XVIII, and XIX are consistent with the structural assignments and are summarized in detail in the Experimental Section. IX was an expected minor product resulting from the competing addition of 2,2,2-trifluoroethoxide anion. The structure and stereochemistry were established by analysis of its N M R spectrum in a manner similar to that described for VI above. Reaction 4 gave the epimeric nitriles XI11 and XIV and also the epimeric ethers XV and XVI. Both nitriles gave the equi-
E I , ~ 'V ~ b~ , E I I ~ 'V~ b, 2.33c 2.10c e e e
d d 1.48',f 1.07g 1.26f
" Pt electrode, tetraethylammonium perchlorate (TEAP, 0.1 M) in acetonitrile solution, vs. Ag/O.l M AgN03. Taken as 0.028 V before the anodic peak potential and 0.029 V before the cathodic peak potential: R. S. Nicholson, Anal. Chem., 38,1406 (1966). From ref 3c. In these cases the oxidation wave was not observed, i.e., >2.0 V. e In these cases the reduction wave was not observed, Le.,
