THE JOURNAL OF VOLUME 33, NUMBER 7
Organic Chemistry” Q C p p r i h; 1968 b y 1he Amntcan Ehsmtcat Socirty
JULY12, 1968
Oxymercuration of Strained Olefins. The Effect of Neighboring Groups’ ARNOLDFACTOR^
AND
T. G. TRAYLOR
Department of Chemistry, Revelle College, University of California at San Diego, La Jolla, California Received July 11, 1967 Additions of acids or mercury salts to norbornenes usually give cis-ezo products. We have studied the effect of neighboring groups such aa endo-5-methylol, endo-5-carboxylate, endo-5-carbomethoxyI endo-5-cyano, and syn-7-methyl01 upon the stereochemistry of oxymercuration of norbornene. Neighboring groups such aa -COOH or -CH20H bring about trans addition. The endo-5-CN or endo-5-COOMe groups participate in the addition only in the presence of water. Treatment of endo-5-carboxynorbornene with aqueous deuteriosulfuric acid brings about trans addition to give the 3-ezodeuteriolactone (VIID) in agreement with the oxymercuration reaction. These results do not reveal the cause of the highly stereospecific cis-ezo additions of mercuric salts and acids to norbornene, but suggest that the demand for cis addition is too small to compete with neighboring-group participation in such additions. The results are consistent with either two-step oxymercuration or concerted addition.
gives cis addition. Evidence has been presented for the occurrence of carbonium ion pairs (11) in such syst e m ~ .(2) ~ Although strained olefins such as.bicycloheptene or bicyclooctene usually add electrophiles with rearrangement,sb or with trans stereochemistry,6b several reagents add in a cis fashion as indicated in eq 3-6 below.
Most electrophilic additions to olefins are considered to proceed through an intermediate three-membered ring ( R complex) which opens with inversion to give trans addition of EY.
&
Several instances of cis addition of such reagents have cis additions also been reported r e ~ e n t l y . ~ -These ~ fall into two substrate categories. (1) Addition of electrophilic reagents to aryl-substituted olefins sometimes
(1) Presented a t the 147th National Meeting of The American Chemical Society, Philadelphia, Pa., April 1964. Although the abstract contains errors in configurations, the data and interpretations prasented a t that meeting were those recorded here. (2) National Institutea of Health Poatdoctoral Fellow, 1963-1964. (3) (a) J. Hine, “Physical Organic Chemistry,” McGraw-Hill Book Co., New York, N. Y., 1962, p 214; (b) J. Chatt, Chem. Rev., 48, 7 (1951). (4) (a) T. G. Traylor and A. W. Baker, Tetrahedron Leu., No. 19, 15 (1959); (b) J . Amer. Chem. SOC.,86, 2746 (1963); (c) T. G. Traylor, ibid., 66, 244 (1964); (d) A. Factor, unpublished reaults. (5) (a) H. Kwart and J. L. Nyce, J . Amer. Chem. SOC.,86. 2601 (1964); (b) H. Kwart and R. K. Miller, ibid., 78, 5678 (1956). (6) K . C. Pande and S. Winstein, Tetrahedron Lett., No. 46, 3393 (1964). (7) J. Meinwald. Y. C. Meinwald, and T. N. Baker, 111, J . Amer. Chem. Soc., 88, 4074 (1964). (8) (a) 9. J. Cristol, W. K. Leifert, D. W. Johnson, and J. B. Jurale, ibid., 84, 3918 (1962); (b) S. J. Cristol, L. K. Gaston, and D. W. Johnson, Tetrahedron Lett., No. 4, 185 (1963); (0) 6 . J. Cristol, N. L. Hauae, and J. s. Meek, J . Amer. Chem. Soc., 78, 674 (1951). (9) M. J. Dewar and R. C. Fahey, ibid., 84, 2012 (1962).
+
&-’
(3ra
Hg(OAc), -+
&z
Br f rearrangedproducts
*
+
rearranged products (6)s
The stereochemistry of oxymercuration has been investigated in a wide variety of cyclic and bicyclic olefins. cis addition has been observed only when the olefin is strained and bicyclic.4b Thus oxymercuration
2607
The Journal of Organic Chemistry
2608 FACTOR ANI) TRAYLOR
or carboxy groups complex with mercuric occurs in a cis manner with n ~ r b o r n e n e s , ~both ~ ~ ~ , ~that ~ - ~hydroxy ~ ions to lead the mercury into the olefins from the same cis and trans with bicyclo [2.2.2]0ctene,~~ and trans with side as the polar group. Therefore an unequivocal c y ~ l o h e x e n e ~or~ other ~ ' ~ simple cyclic olefins.4d The structure proof is needed. limited data available indicate similar behavior for We have used the nmr spectroscopy technique deacid addition^.^^,^^^^^^^ veloped by Anderson and Henry12and others to indicate We have previously s u g g e ~ t e dthat ~ ~ ~these ~ cis the stereochemistry of the reactions studied. additions to strained olefins probably occur by a twoI. Stereochemistry of Ring Closure in 5-endostep path similar t.o that in eq 1. They are proposed Substituted Norbornenes.-To determine the stereoto differ from the trans additions only in the second step chemistry of IV and VI, the products of oxymercurain which frontside S N opening ~ of the a complex betion of bicyclo [2.2.1]hept-2-ene-j-endo-carboxylicacid comes favorable for reasons of strain or steric hindrance. (111) and bicyclo [2.2.1]hept-2-en-j-endo-ylmethanol This paper reports the effects of neighboring groups (V) were i ~ o l a t e d ' 3 and * ~ ~their ~ nmr spectra obtained. on rates and stereochemistry of products from additions I n both IV and VI proton 2 appeared as a simple doublet of acids or mercuric salts to norbornenes. centered a t T 4.71 and 4.88,respectively, with a splitting constant ( J ) of 5.0 Hz. The J values in the norbornyl Results system are well established and are tabulated in Table 1.16-17 Two of the oxymercurations were reported previously.'3~'4 The configuration of the acetomercuri TABLE I H positions
112 43 L3 214
AOOH 111
JHH Ha
0 3-4 5 7.7 2.2-2.3
P
3,5 3,7
CH,---O VI a
group was not proved. Furthermore, the usual assumption that electrophiles attack norbornene from the exo side is not justified in these cases. There is evidencela
0
H (10) J. K. Stille and S. C. Stinson, Tetrahedron, 20, 1387 (1964). (11) (a) N. S. Zefirov, L. P. Prikazohikova, and Yu. K. Yurev, Dokl. Akad. Nauk. SSSR, 162, 869 (1963); (b) ibid., Zh. Obsch. Khim., 86, 822 (1965);(o) ibid., 82, 2744 (1962). (12) M. M. Anderson and P. M. Henry, Chem. Ind. (London), 2053
(1961). (13) H.B. Henbest and B. Nicholls, J . Chem. Soc., 227 (1959). (14) (a) M. Malaiyandi and G. F Wright, Can. J. Chem., 41, 1493 (1963); (b) A. M. Biroks and G. F Wright, J . Amer. Chem. SOC.,6 2 , 2412 (1840).
7-8 8-9 0-1.4
Ref
15 15 16 15 15, 17a,b 12, 17a 7 17a 15 15
Note that J between cis protons is quite large (8 or 9 Hz) compared with the -2 Hz found for the trans protons. Also, although the bridgehead proton (1) couples with the exo proton (3) with a J of 3-4 Hz, it fails to couple with the endo proton ( 2 ) . The coupling constants between vicinal protons in the norbornyl system have been found to agree quite well with those calculated using the Karplus-Conroy relationship18agb between dihedral angle, 4, of vicinal protons and their coupling constant. Equation 10 is as implified version of this relationshiplEc(neglecticg electronegativity and C-C-H bond angle and assuming sp3hybridization and a C-C bond length of 1.543 A). J = 4.22 + 4.5 COS 24 - 0.5 COS 4 (10) Since the coupling constant found in IV and VI, 5.0 Hz, was intermediate between that for cis and trans protons, we suspected that some anomalous effect of the chloromercuri group might be operating. However, reduction with sodium-amalgam in D20,which has been shown4bto go with complete retention of configuration, gave compounds containing one deuterium in whose nmr spectra proton 2 again appeared as a doublet with a splitting constant of 4 . 0 He. Synthesis of these deuterated compounds by deuteriosulfuric acid treatment of the appropriate 5-endoA. L. Anet, Can. J . Chem., S9, 789 (1961). (16) W. D. Kumer, J. N. Schoolery, and F. V. Brutcher, Jr., J . Amer. Chem. Soc., 80, 2533 (1958). (17) (a) P. Laszlo and P. R. Sohleyer, ibid., 86, 2709 (1963);(b) ibid., 86, 1171 (1964). (18) (a) M. Karplus, J . Chem. Phzls., 80, 11 (1959); (b) H. Conroy, "Advances in Organic Chemistry," Vol. 11, Interscience Publishers, Inc., New York, N. Y., 1960,p 265;(0) M. Karplus, J . Amer. Chem. Soc., 86, 2870 (1963). (15) F.
OXYMERCURATION OF STRAINED OLEFINS 2609
Vol. $8, No. 7, July 1968 substituted 2-norbornenes gave products identical with those from the reduction of the mercurials. This indicates that the oxymercuration and the proton addition reactions proceeded with the same stereochemistry.
&+
C02Me
+ygC1
HA-HX Hbr-Hx Hc-Hx
Dihedral angle, deg
Calcd J(Hz)'''
-20
7 5.5
N35 -100
0
HJI decoupled
+%i
C--0
d
IV
VI
Figure 1.-Nuclear
bH2-0 VI
VIIID
The recent investigations of Cristo18 and K w a r P have shown that protons, like all other electrophileslsb add to norbornene from the ex0 side. Thus, on this basis, it would appear that,, in the above deuteriosulfuric acid cases, the proton added ex0 and that the overall stereochemistry of addition to the double bond was trans. This same conclusion was reached by a study of the nmr spectra of undeuterated compounds (Figure 1). I n the spectra of both the lactone and cyclic ether, proton X appeared as a quartet. The exact same quartet was found in the spectra of these compounds run a t 100 Mc on a Varian HR-100 spectrometer,lg showing that the quartet was due to spin-spin splitting. Interpreting this as the X part of an AMX system, it can be concluded that the separation of the outer lines is equal to the sum of J A X and J M X . Since this was 12 HZ and it was found that replacing a proton with mercury or deuterium left a doublet of 5 Hz, it was concluded that the other coupling involved was 7 Hz. From a study of Dreiding models of these cyclized nor(19) We are indebted to Mr. Leroy Johnson, Varian Associates, Pa10 Alto, Calif., for this spectrum.
magnetic resonance spectra of cyclized norbornanes VI1 and VIII.
bornanes, it is possible to estimate the dihedral angles between protons A, &C, !Iand , X and to calculate1* the expected coupling constants. As shown in Figure 1, these calculations indicate that the observed coupling of 5.0 Hz in the mercurials and deuterated compounds is due to coupling between the bridgehead and ex0 protons. This interpretation was substantiated by decoupling the bridgehead proton. Upon irradiation of proton HM the original quartet collapsed to a doublet whose splitting constant was 7 Hz. These results indicate that both the chloromercuri and deuterium groups occupied the ex0 position and that both protonation and oxymercuration proceeded by an electrophilic attack on the exo side of these norbornenes.2'J*21 The vicinial Hglg9-H coupling constants in these compounds agree with this assignmentaZ2 11. The Stereochemistry of Ring Closure with syn7-Hydroxymethyl-2-norbornene.-Recently, Bly and Blyzaahave shown that the oxymercuration of syn-7hydroxymethyl-2-norbornene occurs with ring closure, Professor Bly very kindly sent us a sample of the mercurial for nmr analysis. (20) K. C. Ramey, D. C. Lini, R. M. Moriarty, H. Gopal, and H. G . Walsh [ J . Amer. Chem. SOC., 89, 2401 (1967)l have studied the nmr of VI1 in greater detail and have also assigned the 5-Hzcouplng to HIHL (21) F. R. Jensenand J. J. Miller [TetmhedronLett., No. 40, 4861 (1966)] have recentlyassignedthe same structure to IV on the basis of a comparison of the nmr spectra of IV and its C-3 epimer. However, see ref 20 for proton assignments. (22) M. XI. Kreevoy and J. F. Schaefer. J . Oruanometal. Chem., 6 , 589 (1966). (23) (a) R. K. Bly and R. S. Bly, J . Or& Chem., 28, 3165 (1963); (b) R. S . Bly. R. K. Bly, A. 0. Bedenbaugh, and 0. R. Vail [ J . A m e ~Chem. . Soc., 89, 881 (1967)l have more recently documented this endu mercury attack by obtaining both cia-ezo and tmn8 cyclic mercurials from the oxymercuration of syn-7-(2-hydroxyethyl)norbornene.
2610 FACTOR AND TRAYLOR
The Journal of Organic Chemistry SCHEME I EFFECT OF REACTION CONDITIONS O N THE OXYMERCURATION OF endo-5-CARBOMETHOXY-2-NORBORNENEa
(x)
IlIgCl
nmr HA, 75.25 (doublet, J = 2.3 Hz) HB, 71.0 (multiplet, J = 2 Hz)
1x
The signal from proton A appears as a doublet with J = 2.3 Hz. If proton B were in the cis-endo position, we would expect an AB coupling of 6 or 7 Hz (Table I). The splitting found, 2.3 He, indicates that proton B is in the exo position and that protons A and B are in a trans orientation. The exo assignment for proton B is further substantiated by the complexity of its nmr signal, due to bridgehead ezo proton coupling. Another interpretation of the nmr spectrum of I X is that HAand the 7-anti proton are coupled ( J = 2.3 Hz) and that J A B = 0 He. This would not be unreasonable because the dihedral angle between protons A and B would again be -100" (see Figure 1). Nevertheless, this interpretation again indicates protons A and B to be in a lrans orientation. Thus, we believe that the chloromercuri group must be endo in this mercurial and that the initial mercuric ion attack was in an unprecedented manner from the endo side.23b 111. The Effect of Neighboring Groups on the Oxymercuration of Norbornenes Not Leading Entirely to Ring Closure.-To see if neighboring groups, which did not lead to ring closure, affected the oxymercuration of norbornene, a study was made of the oxymercuration of endo-5-cyano- and endo-5-carbomethoxy-2norbornenes. In Scheme I are summarized the results for the oxymercuration of endo-5-carbomethoxy-2-norbornene (X). HenbestI3 h:is reported that the oxymercuration of this ester in methanol gave exclusively lactone IV; so it was not surprising to find the lactone as the exclusive product when 25% acetone-water was used. However, when carefully dried methanol was used, no lactone was found. The nmr spectrum of the product, a clear liquid, indicated that the signal from proton 3 overlapped with that from an 0-Me group. A careful examination indicated that the downfield Hglg9-H side band consisted of a doublet with J II 7 Hz. Thus it is reasonable that the main peak was a doublet with J 'v 7 Hz and that the major product is likely the cis-exo3-methyl ether (XI.[). Henbest and Nichols13 possibly used wet methanol. Using acetic acid as solvent, oxymercuration of X also afforded no lactone but gave an 80% yield of sharp melting solid the elemental analysis and ir spectrum of which agreed with the 3-acetoxy structure XI (R = Ac). I n the nmr spectrum of this compound proton 3 appeared as a doublet with J = 6.9 Hz indicating that the product had a cis-exo configuration. Thus it is seen that in the oxymercuration of this ester either cis or trans addition can be obtained by making small changes in the solvent. I n the mercuric acetate treatment of endo-5-cyanonorbornene (XIII) , three separate products could be isolated : two sharp-melting crystalline solids and a
-.
X X
-
XI, R= Ac XII, R = Me XI. XI1
IV
25y0 acetone-HZ0
r
HOAc
0% 80% white solid Alp 150.~-151,0" Nmr J2,3 = 6 . 9 Hz
90%
0%
anhydrous MeOH
X
1007, oil, Nmr (Hg'gQ-H side band) J2,3Ei 7 HZ
0%
a X = C1. I n all case8 the product was treated with sodium chloride to obtain the more stable RHgCl.
SCHEME I1 OXYMERCURATION OF €?&&-5-CYANO-2-NORBORNENE
XIV
XI11
HN-)
CN
0
xv MP, "C I r spectrum, p Nmr spectrum, ppm, doublet
XVI
XIV
Xv
XVI
171.5 5.78 5.07 ( J 1 . 3 = 7 . 0 Hz)
154-155 2.75 3.94 (J2,3 = 6 . 9 Hz)
Liquid? 5.85 4.13 (Jl,2= 5 . 0 Hz)
liquid residue. The properties of these products are summarized in Scheme 11. Based on their nmr spectra the solids were assigned the cis-exo configurations shown. Also, acetylation of the alcohol (XV) gave the acetate (XIV). The oil showed a strong absorbtion
6N
xv
eN
XIV
a t 5.85 I.( in the infrared and showed a doublet a t r 5.87 (J2,3= 5.0 He) in its nmr spectrum. This constituent was thought to be the trans lactam shown. That it was not an acetate was obvious from the fact that this product was also obtained with Hg(N03)2. However, efforts to purify t,his component by inducing crystallization or by chromatography on deactivated
OXYMERCURATION OF STRAINED OLEFINS2611
Vol. 33, No. 7, J u l y lg68
79% to 60 and 28%. Such changes in product compoalumina (2% water) have failed, and no sample has sition were observed with n o r b ~ r n e n e ~and ~ l bicyclo~*~~~ been prepared pure enough for elemental analysis. [2.2.2]0ctene.~~ Experiments have shown that Hg(NOa)zfails to react Since XI, XIV, and XV are sharp melting, have sharp with aqueous acetonitrile at room temperature. Also, nmr doublets for proton 3, and are obtained in high the oxymercuration of norbornene in 25% acetonitrile yielded only the exo-cis-2-ch1oromercuri-3-norborneo1, yield, it is felt that only one of the two possible isomers is formed. Because there seems to be no evidence for and no (
