J. Org.Chem. 1981,46,531-538 The kinetic data are listed in Tables 111-VII.
Acknowledgment. We are grateful to Miss Takako Ishibashi for helpful discussions and experimental assistance. Registry No. 6a, 539-80-0; 6b, 3839-48-3; 7, 17346-16-6;8a, 75918-92-2; 8b, 75933-25-4; 8c, 75918-93-3; 12, 75918-94-4; 13,
531
75918-95-5; 14, 75918-96-6; 15, 75933-26-5; 16, 75933-32-3; 18, 75918-97-7; 19b,51932-77-5;208, 75918-98-8; 20b, 75918-99-9; ~OC, 75919-00-5; 20d, 75919-01-6; 24, 75919-02-7; 25, 75919-03-8; 2phenyltropone, 14562-09-5; cycloheptatriene, 544-25-2; 2,5-dimethyl-3,4-diphenylcyclopentadienonedimer, 38883-84-0; 2,5-dipropyl-3,4-diphenylcyclopentadienone, 61202-93-5;2,5-dibutyl-3,4diphenylcyclopentadienone,75919-04-9; 6-(dimethylamino)fulvene, 696-68-4.
Solvomercuration-Demercuration. 8. Oxymercuration-Demercuration of Methoxy-, Hydroxy-, and Acetoxy-Substituted Alkenes' Herbert C. Brown* and Gary J. Lynch2 Richard B. Wetherill Laboratory, Purdue University, West Lafayette, Indiana 47907 Received August 25, 1980
The oxymercuration-demercuration(OM-DM) of a series of methoxy-, hydroxy-, and acetoxy-substituted alkenes was examined. The systems examined were the allyl, crotyl, 3-buten-l-yl, 4-penten-l-yl, and 5-hexen-1-yl. The methoxyalkenes undergo hydration with very high regioselectivity and almost quantitative yield in all cases. However, a small -I effect is observed in the case of the allylalkene (97.1% Markovnikov vs. 99.5% in 1-hexene). Moreover, in the crotyl case, a major directing effect is observed 97.7% 3-01,2.3% 2-01. The other three alkenes undergo the OM reaction with no effect from the methoxy group (99.5% Markovnikov isomer). In contrast, only allyl-, crotyl-, and 3-buten-1-yl alcohols produce major amounts of hydrated products, the diols. While no hydroxyl group directing effect is observed in the allyl system, a major one is again seen in the case of the crotyl: 93.5% 1,3-diol and 6.5% 1,2-diol. The major products from the 4-penten-1-yl and 5-hexen-1-yl alcohols are 2-methyltetrahydrofuran and 2-methyltetrahydropyan, respectively, resulting from OH-5 and OH-6 neighboring group participation in the OM stage. The acetoxy alkenes undergo hydration to give diols in ca. 80% yield with ca.20% unreacted starting material. This is the result of a competitive deoxymercuration reaction which is occurring in the DM stage. However, the yield of hydrated products can be increased by varying the amount of base used in the DM. Neighboring-group participation, Ac0-5, is observed in the allyl system only, resulting in a 65% yield of the Markovnikov oxymercurial, by 'H NMR analysis, and a 35% yield of the acetoxy-exchanged mercurial. Again, a major -1-directing effect of the acetoxy group was observed in the crotyl system but not in the others. In addition to the expected 1,2- and 1,3-diols, the OM-DM of crotyl acetate also resulted in small amounts of the unexpected 2,3-diol under kinetic conditions. Finally, a modified DM procedure has been developed which is compatible with the acetoxy group.
The oxymercuration-demercuration (OM-DM) of olefins is an extraordinarily valuable method for the Markovnikov hydration of olefins and dienes with remarkably high regi~selectivity.',~For example, 1-hexene undergoes reaction to give a 94% yield of alcohols, a 99.5% yield of 2-hexanol and a 0.5% yield of 1-hexanol (eq 1).
Chart Ia X
c=c-c
l
c-c=c-c
(1) The oxymercuration-demercuration of unsaturated alcohols was discussed earlier in connection with a study of the reaction of dienes: H. C. Brown, P. J. Geoghegan,Jr., J. T. Kurek, and G. J. Lynch, Organornet. Chern. Synth., 1, 7 (1970). (2) Texaco research fellow at Purdue University, 1972-1973. Graduate research assistant, 1969-1972, on a study supported by a grant from the Esso Research and Engineering Co. (3) H. C. Brown and P. J. Geoghegan, Jr., J. Org. Chern., 35, 1844 (1970). (4) J. L. Jernow, D. Gray, and W. D. Closson, J. Org. Chern. 36,3511
(1971). (5) M. Barelle and M. Apparu, Bull. SOC.Chin. Fr., 2016 (1972). (6) H. Christol, F. Plhat, and J. Revel, Bull. SOC. Chirn. Fr., 4537 (1971). (7) J. A. Soderquist and K. L. Thompson,J. Organornet. Chern., 159, 237 (1978).
0022-3263/81/1946-0531$01.00/0
x
I
4
While there are numerous examples in the literature on the OM-DM of functionally substituted alkenes, there are but a few detailed, systematic ~tudies.~-'OConsequently,
3
X I
a
i
c=c-c-c
2
1
c=c-c-c-c CH3(CHJ3C(OH)HCH3 (1)
i
c=c-c-c-c-c
I I
5 X = OCH,, OH, OAc.
we undertook such a study on representative functionally substituted acyclic alkenes. The results are detailed and discussed in this as well as the following paper in this series. Results and Discussion The alkene systems examined were the allyl (l),crotyl (2; 2-buten-l-yl), 3-buten-1-yl (3), 4-penten-1-yl (4), and 5-hexen-l-y1(5)with the methoxy, hydroxy, and acetoxy functional groups (Chart I). (8) F. D. Gunstone and P. R. Inglis, Chem. Phys. Lipids, 10, 73, 89, 105 (1973). (9) Much of the earlier work on the oxymercuration stage has been reviewed; see ref 10. (10) W. Kitching, Organornet. Chern. Rev., 3, 61 (1968).
0 1981 American Chemical Society
Brown and Lynch
532 J Org. Chem., Vol. 46, No. 3, 1981
Table I. Oxymercuration-Demercuration of Methoxy Substituted Olefins _______ 9i yieldC product distribution of methoxy R of ROMe t,,as t 2 , b min alcohols product %C allyl f 10 30 94 1-methoxy-2-propanol 97.1 1-methoxy-3-propanol 2.9 3-buten-1-yl 14 30 97 4-methoxy- 2-butanol 99.1 4-methoxy-1-butanol 0.9 crotyl 35 30 100 4-methoxy-2-butanol 97.7 1-methoxy-2-butanol 2.3 99.8 4-penten-1-ylg 15 30 9 5d 5-methoxy-2-pentanol 5-methoxy-1-pentanol 0.2 5-hexen-l-ylh 12 30 93e 6-methoxy-2-hexanol 99.8 6-methoxy-1-hexanol 0.2 a Time for the yellow color to disappear. Complete time for OM stage. By VPC analysis. Small amounts of residual olefinic ether was observed in the product but was not quantitatively analyzed. e 6% of residual 6-methoxy-lN o 2-methoxy-1-propanol could be detected in the product. g N o 4-methoxy-lhexene was present in the product. N o 5-methoxy-1-hexanol or 2-methyltetrahydropentanol or 2-methyltetrahydrofuran could be detected in the product. pyran could be detected in the product.
__- - ---
Scheme I
10
HO
12
Methoxy-Substituted Alkenes. These alkenes undergo hydration in all cases in nearly quantitative yield and with very high regioselectivity. The only products observed are the methoxy alcohols. The results are summarized in Table I. The allylalkene undergoes hydration with very high Markovnikov regioselectivity, 97.1 % . Nevertheless, it is lower than that observed for a typical monosubstituted olefin such as 1-hexene. This is readily attributable to the -I effect of the methoxy group. However, in the case of crotyl, where both carbon atoms are substituted, a major directing effect is observed. Gunstone and Inglis6have also observed a similar directing effect in the OM-DM of several methoxy-substituted, unsaturated, fatty acid esters. It is also significant that no evidence of neighboringgroup participation by the methoxy group was observed. Moreover, in a study on the methoxymercuration-demercuration of 4-penten-1-yl and 5-hexen-1-ylmethyl ethers by Pritzkow and co-workers,*l a similar conclusion was reached. On the other hand, Closson and co-workers4have reported that the OM-DM of 5-methoxycyclooctene (6) gives two bicyclic ethers (8 and ll),apparently arising from neighboring-group participation (Scheme I). Consequently, the OM-DM of 6 was reinvestigated. No products arising from neighboring-group participation (i.e.,
8 and 11) could be detected, however. The only products observed appeared to be methoxycyclooctanols.12 Hydroxy-Substituted Alkenes. The results of the OM-DM of these alkenes are summarized in Table 11. High yields of the hydrated products, the diols, are obtained from the allyl, crotyl, and 3-buten-1-yl alkenes. In
(11) V. B. Beyer, C. Duschek, H. J. Franz, R. Hahn, W. Hobold, P. Kluge, W. Pritzkow, and H. Schmidt, J . Prakt. Chern., 312,622 (1970).
(12) These compounds are identified on the basis of VPC retention times.
Scheme I1
ACOH< HgiOAc12
.t
J. Org. Chem., Vol. 46, No. 3, 1981
Solvomercuration-Demercuration
533
Table 11. oxy mercuration-Demercuration of Unsaturated Alcohols product distribution R of ROH allyl
t,,a 3
3-buten-1-yl
6
crotyl
min 30
t,,b
30
product 1,2-propanediol 1,3-propanedi 01 1,3-bu tanedi 01 1,4-bu tanedi 01 tetrahydrofuran 1,3-butanediol 1,2-butanediol 2-methyltetrahydrofuran 1,4-pentanediol 1,5-pentanediol
75 (97) 87 (93) 84 (93)
%C
99. oe
l.oe
99.2
0.7 O.lf
93.5 6.5 99.4 4-penten-1-yl 5 30 95 0.6 trace 91.9 5-hexen-1-yl 7 30 100 2-methyltetrahy dropyran 8.1 1,5-hexanediol trace 1,6-hexanediol a-c See corresponding footnotes in Table I. Total VPC yield of all products listed. Numbers in parentheses are based on a continuous extraction procedure for diol product isolation. Numbers not enclosed in parentheses refer t o a multiple simple extraction procedure. e These isomer distributions have been corrected for the fact that the efficiency of recovery of the 1,3-propanediol diacetate from a blank OM-DM is only 0.6 of that for the 1,2-propanediol diacetate. Determined from a run made in pure water with no THF solvent. 12
30
% yieldcSd
Table 111. Oxymercuration-Demercuration of Acetoxy-Substituted Olefins % yield residual diol distribution, 5% t,,b reduction unsaturated R o f ROAc s rnin conditionsC alcoholsd diolsdie 1,2 1,3 2,3 1,4 195 allyl 30 30 normal 14 (80) 99.2f O.Bf 60 normal 18 (77) 30 4.5MNaOH 1 (92) 99. 2f 0. Bf 30 4.5MNaOH 1 62 3-buten-1-yl 14 30 normal 28 64 98.8 1.2 30 4.5M NaOH 6 82 99.0 1.0 crotyl 90 30 normal 12g + 6h 77 6.7 91.9 1.4 30 4.5MNaOH 6g + lh 89 5.6 92.9 1.5 4-penten-1-yl 1 5 30 normal 16-18 67-80 100' 8 60-70 100 30 4.5MNaOH 30 4 . 5 M N a O H + 8 67-70 100 30 rnin of stirring' 30 4 . 5 M N a O H + , 4 90 100 30 rnin of reflux' 30 noNaOHh 5 89 100 5-hexen-1-yl 24 30 normal 5 87 10om See corresponding footnotes in Table 11. Normal refers to the standard procedure, whereas, 4.5 M NaOH refers to the By VPC analysis. the substitution of 4.5 M NaOH for the 3.0 M NaOH in the reduction stage of the standard procedure. e Total VPC yield of diols. Numbers in parentheses are based on a continuous extraction procedure for diol product extraction. Numbers not in parentheses refer to a multiple simple extraction procedure. f Corrected for relative recovery 3-Buten-2-01. I 4.5 M NaOH was used in the reduction stage and, the reaction solution efficiencies. g Crotyl alcohol. stirred for 30 min after the 4.5 M NaOH had been added, before addition of the NaBH, solution. 4.5 M NaOH was used in the reduction stage and the reaction solution refluxed for 30 min after the 4.5 M NaOH had been added, before addition No NaOH solution was used to initiate the reduction stage; the NaBH, solution was added of the NaBH, solution. No (< 3%) 2-methyltetrahydropyran directly. No (
