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Gallium-mediated highly regioselective reactions of trimethylsilylpropargyl bromide and trimethylsilylallyl bromide with carbonyl compounds
Tctmhedmn Liters, VoL 35. No. XI, pp. 9433-9434, 1994 Elsevia science Lad Printed in Great Britain -9/94 $7.m*o.o0
00404039(94)02090-6
Reactions of Trimethylsilylpropargyl Bromide and Trimethyfsilylallyl Bromide with Cwbonyl Compounds
Gallium-Mediated Highly Regbselective
Yinp Han
Yao-Zeng
Hung*
Labaratory ofOtganometdlic Chemistry, Shaagh8i Tntitute of Organic Chcmisuy.ChineseAcademyof L%2cnca354 Fen&n Lu,
shanghaizGiuJ32. china
At&met:
One-pot reactions of gallium powder. trimethylsilylpropargyl bromide, aldehydes or ketones in the presence ofKI and LiCl show very high acetylenic s&ctivity and under the same conditions,trimethylsilylallyl bromide also exhibits very high selectivity favoring CMdducts.
Methods for selective nucleophilic propargylation or allylation of carbonyl compounds remain an impoM AUenyI and propargyl metal derivatives are in equilibrium in solution and these isomers react dif&rently with carbonyl compounds, The regioselectivity is dependent on the kind of metal. For example, Zn’ and Sb* reagents show acetyienic selectivi~, while Al’ reagents exhibit aknic selectivity. The regioselectivities of trimethylsilylaHyl organometallic reagents towards carbonyl compounds are also dependent on the kind of metaI, e. g. Li and Zn3 show a-adducts. B’, Ti’ and the recent descfibed Cr’ exhibit y-adducts. However, their regioselectivities are not very high.We noticed that the organogaIIium compounds and metallic gallium6 itself have been scarcely used for synthetic purposes. Herewith we report our findings. Tbe trimetbyIsily1prop@ gallium reacted with a variety of aldehydes or ketones in &wing THF in the presence of KI and LiCl or Lewis acids ( MgBr, and BFJ OEt2 ) to give, afhx subsequent hydrolysis, h~n~~propgylic alcohols exclusively in high topic of research in organic chdstry.
yields as shown in ‘Table 1,
1
2
3
Aromatic aldehydes, aliphatic aldehydes and ketones regio&ctively gave corresponding bmopropargylic alcohols in high yield@3 < 3%), while Sb’ reagent gave a mixture of 2 and 3. The yields of Zn’ reagent reacting with carhonyl compounds was moderate, 2:3 = 90: 10, when the substrate was cycIohexylaidehyde. Furthermore, we fbundthe yietd d this reaction could be improved greatly by the addition ofLiC!l or Lewis acids, such as, Mg.Br2 and BF3 OEt2, without aitering the regiosekctivity. Wrthwt LiCl or Lewis acid the reaction progressed sluggishly only in the yield of 18% even by refluxing for IO hrs. Although the reason for Lewis aoids to improvethe yield has not yet been clarified, it presumably involves thar the coordination of lithium ion or Lewis acids to carbony group results in activating the carbonyl group and increa&g the yield. Under the same conditions, gaflium can also promote the reaction of trime$hylsilyiallyl bromide and
c&onyl compounds. Only a-adducts’ were obtained in excellent yields ( see Table 1).
9434
The ratios of E- and Z-isomer of products were genaally greater than 90: 10 ( except for Entry 9 and IO ) of the isomer proportion of starting material trimethylsilyldlyl bromide ( E/Z = 96:4 or 37:63 ). The following experimental procedure is typic& Into a suspension of gallium powde@hg,1.2tnmo~) in THF was added potassiutn iodide(249mg ,I .S mmol ) , lithium chloride (42.5 mg , 1 mm01 ) ,trimethylsillylpro~l bromide ( 286.5mg. 1.5mmol ) and 4xhlorobenzaldehyde( 140_5mg, lmmol ). The mixture was r&axed for 2h under argon. Al& the usual work-up,1-(4-chlorophenyl)4(trimethylsiyl)-3-butynol was obtained in 99?%1 yield. irrespective
Table 1. Selective Syntbses of Homopropargylic Alcohols’ and Homoallylic Alcohols”
Entry
RR’CO
1
C&&HO
2 3 4 5 6 7 8 9
p-CH_GWXO
Time(h) Product ratjob Total yield’ (2f3) (%I
p-ClCsHKHO pFC#+CHO C&CH=CHCHO c-Cd&CHO~
r&H, ,CHO n-&H&HO (CH&CD 10 C&l,COCH3 11 p-B&H&HO 12 P-naphthaldehyde
2 2 2 2 3 3 3 5 S 5
?39:1 *9:1 >99: 1 299: 1 98:2 98:2 97:3 149:1 >99: 1 39: 1
Time(h) ’ Product rati$ (415)
92 97 99 91 78 89 87 82 85 87
Total yield’ (%I
2 2 1.5
91:9(91:9)d 9Q:lO 92:8(92:8)
95193) 92 96c97)
2
91:9
95
2 2 1.5 2
85:15(85: 15) Qww 85.15 91 91~9 94 9O:lO 90
we= paformed as descrii in the text. All ofknown mlnpounds gave WkfacWy ‘H NMIZand IR of MS, unknown compmnds geve sattsfacIoryspectral and element ana@iCal data. b). Determinedby 3oOMHz ‘H NMR analysis. c). Isolatedyield based on aldehydes. Unless otherwise no&d. the E/Z ratioof thetimethylsilylauylbromideusedas s@lting material WBS%:4. d), “k data in the parentheses show the results when trimethyltilylallyl bromide as the ~tmting material~E:Z=37:Cf). a). All the t-e&cm
Acknowledgement: Thanks are due to the National Natural Science Foundation of China and Academia Sinica for financial support. References rnd notes: 1. Da&Is, R.G.; Paquette, L A., Tetruhe&onLetf., 1981, 22, 1579. 1. L.,Huang, Y.Z., Te?rahe&onL.etl., 1993, 34, 1621 2. Zhang,L.J.;Mo,XS.;Husng, 3. Ehlinqtr, M. P., J. Am. Chem. Sot., 1980, 102,5004. 4. Reets, M. T., Zbp. Curr. Ckm. 1932, 106, 1, 5. Ho&son D. M.; Wells C., Tdmhe&~z Zrert.,1992, 33, 4761. 6. (a).G. Zweifel. “&ganic £s of Group 3 Metals,” in “Comprehettdve Ogunic Uwmhtry,” d by Derek H. R. Bartonand W. D. Otis, PergamonPresq Oxford ( 1979 ). Vol. 3. Part 15.3, pp 1013-1041. b).Araki, K., Ito, H., Butsugan, Y., Appr.~e:.c7~~.~ l-,4757. 7 _The gallium-promoted reaction of crotylbromide with aldehydes gave y-adduc! excl&vely.
(Received in Chhu 23 July 1994; accepted 29 September 1994)
00404039(94)02090-6
Reactions of Trimethylsilylpropargyl Bromide and Trimethyfsilylallyl Bromide with Cwbonyl Compounds
Gallium-Mediated Highly Regbselective
Yinp Han
Yao-Zeng
Hung*
Labaratory ofOtganometdlic Chemistry, Shaagh8i Tntitute of Organic Chcmisuy.ChineseAcademyof L%2cnca354 Fen&n Lu,
shanghaizGiuJ32. china
At&met:
One-pot reactions of gallium powder. trimethylsilylpropargyl bromide, aldehydes or ketones in the presence ofKI and LiCl show very high acetylenic s&ctivity and under the same conditions,trimethylsilylallyl bromide also exhibits very high selectivity favoring CMdducts.
Methods for selective nucleophilic propargylation or allylation of carbonyl compounds remain an impoM AUenyI and propargyl metal derivatives are in equilibrium in solution and these isomers react dif&rently with carbonyl compounds, The regioselectivity is dependent on the kind of metal. For example, Zn’ and Sb* reagents show acetyienic selectivi~, while Al’ reagents exhibit aknic selectivity. The regioselectivities of trimethylsilylaHyl organometallic reagents towards carbonyl compounds are also dependent on the kind of metaI, e. g. Li and Zn3 show a-adducts. B’, Ti’ and the recent descfibed Cr’ exhibit y-adducts. However, their regioselectivities are not very high.We noticed that the organogaIIium compounds and metallic gallium6 itself have been scarcely used for synthetic purposes. Herewith we report our findings. Tbe trimetbyIsily1prop@ gallium reacted with a variety of aldehydes or ketones in &wing THF in the presence of KI and LiCl or Lewis acids ( MgBr, and BFJ OEt2 ) to give, afhx subsequent hydrolysis, h~n~~propgylic alcohols exclusively in high topic of research in organic chdstry.
yields as shown in ‘Table 1,
1
2
3
Aromatic aldehydes, aliphatic aldehydes and ketones regio&ctively gave corresponding bmopropargylic alcohols in high yield@3 < 3%), while Sb’ reagent gave a mixture of 2 and 3. The yields of Zn’ reagent reacting with carhonyl compounds was moderate, 2:3 = 90: 10, when the substrate was cycIohexylaidehyde. Furthermore, we fbundthe yietd d this reaction could be improved greatly by the addition ofLiC!l or Lewis acids, such as, Mg.Br2 and BF3 OEt2, without aitering the regiosekctivity. Wrthwt LiCl or Lewis acid the reaction progressed sluggishly only in the yield of 18% even by refluxing for IO hrs. Although the reason for Lewis aoids to improvethe yield has not yet been clarified, it presumably involves thar the coordination of lithium ion or Lewis acids to carbony group results in activating the carbonyl group and increa&g the yield. Under the same conditions, gaflium can also promote the reaction of trime$hylsilyiallyl bromide and
c&onyl compounds. Only a-adducts’ were obtained in excellent yields ( see Table 1).
9434
The ratios of E- and Z-isomer of products were genaally greater than 90: 10 ( except for Entry 9 and IO ) of the isomer proportion of starting material trimethylsilyldlyl bromide ( E/Z = 96:4 or 37:63 ). The following experimental procedure is typic& Into a suspension of gallium powde@hg,1.2tnmo~) in THF was added potassiutn iodide(249mg ,I .S mmol ) , lithium chloride (42.5 mg , 1 mm01 ) ,trimethylsillylpro~l bromide ( 286.5mg. 1.5mmol ) and 4xhlorobenzaldehyde( 140_5mg, lmmol ). The mixture was r&axed for 2h under argon. Al& the usual work-up,1-(4-chlorophenyl)4(trimethylsiyl)-3-butynol was obtained in 99?%1 yield. irrespective
Table 1. Selective Syntbses of Homopropargylic Alcohols’ and Homoallylic Alcohols”
Entry
RR’CO
1
C&&HO
2 3 4 5 6 7 8 9
p-CH_GWXO
Time(h) Product ratjob Total yield’ (2f3) (%I
p-ClCsHKHO pFC#+CHO C&CH=CHCHO c-Cd&CHO~
r&H, ,CHO n-&H&HO (CH&CD 10 C&l,COCH3 11 p-B&H&HO 12 P-naphthaldehyde
2 2 2 2 3 3 3 5 S 5
?39:1 *9:1 >99: 1 299: 1 98:2 98:2 97:3 149:1 >99: 1 39: 1
Time(h) ’ Product rati$ (415)
92 97 99 91 78 89 87 82 85 87
Total yield’ (%I
2 2 1.5
91:9(91:9)d 9Q:lO 92:8(92:8)
95193) 92 96c97)
2
91:9
95
2 2 1.5 2
85:15(85: 15) Qww 85.15 91 91~9 94 9O:lO 90
we= paformed as descrii in the text. All ofknown mlnpounds gave WkfacWy ‘H NMIZand IR of MS, unknown compmnds geve sattsfacIoryspectral and element ana@iCal data. b). Determinedby 3oOMHz ‘H NMR analysis. c). Isolatedyield based on aldehydes. Unless otherwise no&d. the E/Z ratioof thetimethylsilylauylbromideusedas s@lting material WBS%:4. d), “k data in the parentheses show the results when trimethyltilylallyl bromide as the ~tmting material~E:Z=37:Cf). a). All the t-e&cm
Acknowledgement: Thanks are due to the National Natural Science Foundation of China and Academia Sinica for financial support. References rnd notes: 1. Da&Is, R.G.; Paquette, L A., Tetruhe&onLetf., 1981, 22, 1579. 1. L.,Huang, Y.Z., Te?rahe&onL.etl., 1993, 34, 1621 2. Zhang,L.J.;Mo,XS.;Husng, 3. Ehlinqtr, M. P., J. Am. Chem. Sot., 1980, 102,5004. 4. Reets, M. T., Zbp. Curr. Ckm. 1932, 106, 1, 5. Ho&son D. M.; Wells C., Tdmhe&~z Zrert.,1992, 33, 4761. 6. (a).G. Zweifel. “&ganic £s of Group 3 Metals,” in “Comprehettdve Ogunic Uwmhtry,” d by Derek H. R. Bartonand W. D. Otis, PergamonPresq Oxford ( 1979 ). Vol. 3. Part 15.3, pp 1013-1041. b).Araki, K., Ito, H., Butsugan, Y., Appr.~e:.c7~~.~ l-,4757. 7 _The gallium-promoted reaction of crotylbromide with aldehydes gave y-adduc! excl&vely.
(Received in Chhu 23 July 1994; accepted 29 September 1994)