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Journal of the Brazilian Chemical Society

Print version ISSN 0103-5053On-line version ISSN 1678-4790

J. Braz. Chem. Soc. vol.16 no.3b São Paulo May/June 2005

https://doi.org/10.1590/S0103-50532005000400002 

COMMUNICATION

 

b-butyltellanyl carbonyl compounds: a useful source of masked metal homoenolates

 

Alcindo A. dos Santos*; João V. Comasseto

Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, nº 748, 05508-900 São Paulo - SP, Brazil

 

 


ABSTRACT

Secondary higher order cyanocuprates and lithium homoenolates, were efficiently generated from b-butyltellanylketals and reacted with benzaldehyde and 2-cyclohexen-1-one.

Keywords: tellurides, tellurium / lithium exchange, secondary lithium homoenolates and higher order cyanocuprates


RESUMO

Cianocupratos de ordem superior e homoenolatos de lítio secundários, foram eficientemente gerados a partir de b-butil teluro cetais e submetidos a reação com benzaldeido e 2-cicloexen-1-ona.


 

 

Introduction

Homoenolate anions are important synthons in the Umpolung concept.1 Unlike the enolate anions, the homoenolate anions cannot be stoichiometrically generated by deprotonation of a carbonyl compound, since the pka value of the b-hydrogen is only very slightly lowered.2 In addition, the reactive homoenolates 1, especially lithium and sodium derivatives, spontaneously cyclize to the corresponding cyclopropanolate tautomer 2 (Scheme 1),2 which does not react as a carbon-nucleophile with standard electrophiles.

 

 

Although the a-enolization of carbonyl compounds is readily carried out under mild conditions to yield high equilibrium concentrations of a-enolates, vigorous conditions are required to give low concentrations of short-lived intermediate homoenolates by b-deprotonation of nonenolizable ketones.2 This fact makes the direct b-deprotonation of carbonyl compounds an impracticable method for preparative purposes. The use of a masked carbonyl unit is an alternative to circumvent this problem.3 However, this strategy is also limited to the presence of strongly electron-attracting substituents at the b-position to the masked carbonyl groups that promotes the stabilization of the carbanion formed. Classically, for this purpose nitro,4 phosphorus5 and sulphur6 based compounds are used. Moreover, this method requires previous preparation of the nitro, phosphorus or sulphur organic substrates and another further step, to remove reductively the activating group.

A simple strategy to circumvent this problem should be the preparation of b-butyltellanyl masked carbonyl compounds such as 3,7 and their transformation into the corresponding lithium homoenolates through a tellurium/lithium exchange reaction (Scheme 2).8

 

 

A general way to obtain compounds of type 3 should be the Michael addition of n-butyltellurol to a,b-unsaturated ketones, as recently described by us,9 followed by a ketalization reaction.

The n-butyltellurol, generated in situ by reaction of elemental tellurium with n-BuLi in THF, followed by addition of a proton source such as ethanol or water, reacts rapidly with Michael acceptors.9 Under these conditions the b-butyltellanylketones 5 and 6 were successfully prepared in 86% and 89% yield respectively (Scheme 3).

 

 

The b-butyltellanylketones 5 and 6 were converted into the corresponding b-butyltellanylketals 3 and 7 in high yields by reaction with ethylene glycol in benzene in a Dean-Stark apparatus (Scheme 4).9,10

 

 

The light yellow tellurides 3 and 7 were transformed into the corresponding lithium masked homoenolates by reaction with t-butyllithium in THF at –70 ºC. The tellurium/lithium exchange showed to be very fast even to generate a secondary anion.

Trapping the lithium anions with benzaldehyde afforded the corresponding alcohols 8 and 10 (Scheme 5).11 The lithium intermediates were also submitted to reaction with the copper soluble species CuCN.2LiCl12 producing the corresponding higher order cyanocuprates.13 Michael addition of these intermediates to 2-cyclohexen-1-one produced the corresponding saturated ketones (Scheme 5).13

 

 

All tellurides described in this paper are stable to the ambient light and can be manipulated in the air. Most of them are almost odourless or present a smell not more unpleasant them most of the laboratory chemicals normally used in an organic synthesis laboratory.

It is worthy of note that the dibutyltelluride originated in the tellurium/lithium exchange step, is totally compatible with all the subsequent operations. It can be easily eliminated in an odourless operation by washing the organic phase with a diluted sodium hypochlorite solution.

In conclusion, b-butyltellanyl carbonyl compounds are a very practical source of homoenolate equivalents.

 

Acknowledgements

The authors thank FAPESP for support.

 

References

1. Seebach, D.; Angew. Chem. Int. Ed. Engl. 1979, 18, 239;         [ Links ]Evans, D. A.; Andrews, G. C.; Acc. Chem. Res. 1974, 7, 14;         [ Links ]Hoppe, D.; Angew. Chem. Int. Ed. Engl. 1984, 23, 932.         [ Links ]

2. Werstiuk, N. H.; Tetrahedron 1983, 39, 205;         [ Links ]Ryu, I.; Sonoda, N.; J. Syn. Org. Chem. Jpn. 1985, 43, 112;         [ Links ]Nakamura, E.; J. Syn. Org. Chem. Jpn. 1989, 47, 931.         [ Links ]

3. Büchi, G.; Wüest, H.; J. Org. Chem. 1969, 34, 1122;         [ Links ]for a recent review see: Yus, M.; Torregrosa, R.; Pastor, I. M.; Molecules 2004, 9, 330.         [ Links ]

4. Bakuzis, P.; Bakuzis, M. L. F.; Weingartner, T. F.; Tetrahedron Lett. 1978, 2371;         [ Links ]Crumbie, R. L.; Nimetz, J. S.; Mosher, H. S.; J. Org. Chem. 1983, 47, 4040;         [ Links ]Corey, E. J.; Vlattas, I.; Anderson, N. H.; Harding, K.; J. Am. Chem. Soc. 1968, 90, 3247.         [ Links ]

5. Corey, E. J.; Shimoji, K.; J. Am. Chem. Soc. 1983, 105, 1662;         [ Links ]Bell, A.; Davidson, A. H.; Earnshaw, C.; Norrish, H. K.; Torr, R. S.; Warren, S.; J. Chem. Soc. Chem. Comm. 1978, 988;         [ Links ]Cristau, H. J.; Chabaud, B.; Niangoran, C.; J. Org. Chem. 1983, 48, 1527.         [ Links ]

6. Kondo, K.; Tunemoto, T.; Tetrahedron Lett. 1975, 1007;         [ Links ]Fayos, J.; Clardy, J.; Dolby, L. J.; Farham, T.; J. Org. Chem. 1977, 42, 1349.         [ Links ]

7. The generation of 3 by a different approach and its transformation into a lithium homoenolate has been already described: Inoue, T.; Atarashi, Y.; Kambe, N.; Ogawa, A.; Sonoda, N.; Synlett 1995, 209.         [ Links ]

8. Hiiro, T.; Kambe, N.; Ogawa, A.; Miyoshi, N.; Murai, S.; Sonoda, N.; Angew. Chem. Int. Ed. Engl. 1987, 26, 1187;         [ Links ]for recent reviews see: Comasseto, J. V.; Barrientos-Astigarraga, R. E.; Aldrichimica Acta 2000, 33, 66;         [ Links ]Petragnani, N.; Stefani, H. A.; Tetrahedron 2005, 61, 1613.         [ Links ]

9. Zinn, F. K.; Righi, V. E.; Luque, S. C.; Formiga, H. B.; Comasseto, J. V.; Tetrahedron Lett. 2002, 43, 1625.         [ Links ]

10. General procedure for the preparation of the b-butyltellanylketalls 3 and 7: To a two bottomed flask equipped with a Dean-Stark reflux apparatus were added the appropriate b-butyltellanylketone 5 or 6 (5 mmol), benzene (10 mL), ethylene glycol (8 mmol, 0.44 mL) and Amberlist® (30 mg). The reaction mixture was refluxed under nitrogen atmosphere for 5 hours. The mixture was filtered and the residue washed with ethyl acetate. The solvents were removed under reduced pressure. The residue was purified by silica gel chromatography eluting with a mixture of hexane:ethyl acetate (15:1), to give 2-(2-(butyltellanyl)ethyl)-2-methyl-1,3-dioxolane (3). Yield: 1.43 g (96%); 1H NMR: (300 MHz, CDCl3, ppm) d 3.95 (m, 4 H); 2.60-2.66 (m, 4 H); 2.10-2.16 (m, 2 H); 1.72 (quint, J 7.3 Hz, 2 H); 1.38 (sext, J 7.3 Hz, 2 H); 1.32 (s, 3H); 0.92 (t, J 7.3 Hz, 3H); 13C NMR: (75 MHz, CDCl3, ppm) d 110.2; 64.7; 42.1; 34.2; 25.0; 23.5; 13.3; 2.7; -5.6; LRMS m/z (rel. int.) 302 (M+, 3); 99 (4); 87 (100); 55 (15); 43 (58); IR (film) nmax /cm-1: 2979; 2958; 2927; 2874; 1457; 1378; 1246; 1212; 1040; 944; 125Te NMR (CDCl3, 157.79 MHz / 298 K / Ph2Te2) d (ppm) 263.3; Anal. Calc. for C10H20O2Te: C, 40.13; H, 6.68; Found: C, 40.35; H, 6.46. 7-butyltellanyl-1,4-dioxaspiro [4.5]hexane (7). Yield: 1.49 g (92%); 1H NMR: (300 MHz, CDCl3, ppm) d 3.94 (t, J 0.8 Hz, 4 H); 3.30 (m, 1 H); 2.66 (t, J 7.2 Hz, 2 H); 2.00-2.23 (m, 2 H); 1.50-1.90 (m, 8 H); 1.37 (sext, J 7.2 Hz, 2H); 0.91 (t, J 7.2 Hz, 3H); 13C NMR: (75 MHz, CDCl3, ppm) d 108.7; 64.2; 44.8; 35.5; 34.5; 34.4; 25.2; 25.0; 16.1; 13.4; 2.3; LRMS m/z (rel. int.) 328 (M+, 10); 141 (87); 99 (100); 79 (12); 69 (18); 57 (13); 55 (44); 41 (70). IR(film) nmax/cm-1: 2953; 2933; 1448; 1356; 1299; 1164; 1063; 1025; 125Te NMR (CDCl3, 157.79 MHz / 298 K / Ph2Te2) d (ppm) 423.31; Anal. Calc. for C12H22O2Te: C, 44.30; H, 6.76; Found: C, 44.49; H, 6.72.

11. Typical procedure for the tellurium / lithium exchange reaction and capture of the resulting organolithium with benzaldehyde: to a solution of telluride 3 (1 mmol, 0.29 g) in THF (5 mL), at -70 ºC was added t-butyllithium (1.0 mmol, 0.89 mL, 1.12 mol L-1 in pentane). After 5 min was added benzaldehyde (1 mmol, 0.1 mL). The reaction mixture was allowed to warm to 0 ºC. The mixture was stirred for 1 h and then diluted with ethyl acetate (5 mL). The organic phase was sequentially washed with a diluted solution of sodium hypochlorite (2 x 5 mL) and brine (2 x 5 mL), dried over magnesium sulphate, filtrated and evaporated. The residue was purified by column chromatography on silica gel using a 2:1 hexane:ethyl acetate mixture as eluent, to give 3-(2-methyl-1,3-dioxolan-2-yl)-1-phenylpropan-1-ol (8). Yield: 0.18 g (84%); CAS Nº: 167644-51-1.

12. Knochel, P.; Yeh, M. C. P.; Berk, S. C.; Talbert, J.; J. Org. Chem. 1988, 53, 2390.         [ Links ]

13. Typical procedure to prepare the higher order cyanocuprate and its reaction with 2-cyclohexen-1-one: To a solution of the lithium anion of telluride 7 (1 mmol, 0.32 g, generated by the same procedure described in ref. 11) at -70 ºC, was added a solution of CuCN.2LiCl (0.5 mmol, 1 mol-1 / THF, 0.5 Equiv.). The resulting orange solution was stirred for 20 min at the same temperature and then 2-cyclohexen-1-one (1 Equiv.) was added in one portion. The resulting solution was stirred for 1 h at -70 ºC and then allowed to warm to 0 ºC. A solution of saturated aqueous ammonium chloride and ammonium hydroxide was added (3 mL) and the mixture was stirred for 40 min. The organic phase was sequentially washed with a diluted solution of sodium hypochlorite (2 x 5 mL) and then with brine (2 x 10 mL), dried over magnesium sulphate, filtered and the solvents were removed. The residue was purified by silica gel chromatography using a 3:1 hexane:ethyl acetate mixture, to give a diastereomeric mixture of 3-(1,4-Dioxa-spiro[4.5]dec-7-yl)-cyclohexanone (11). Yield: 0.19 g (80%); 1H NMR: (300 MHz, CDCl3, ppm) d 3.92-3.94 (m, 4H); 2.22-2.50 (m, 3 H); 2.04-2.13 (m, 2 H); 1.04-1.7 (m, 12 H); 0.86-0.98 (m, 1 H); 13C NMR: (75 MHz, CDCl3, ppm) d 212.1; 109.4; 64.3; 64.2; 45.4; 44.0; 43.9; 41.5; 40.3; 38.7; 38.5; 34.9; 34.8; 28.5; 28.4; 28.3; 25.5; 25.4; 23.2; 23.1; LRMS m/z (rel. int.) 238 (M+, 2); 195 (3); 141 (100); 113 (11); 112 (12); 99 (90); 86 (28); 55 (33); 42 (16); 41 (41); IR(film) nmax /cm-1: 2938; 2866; 1711; 1448; 1355; 1159; 1085; 919; 516; Anal. Calc. for C14H22O3: C, 70.49; H, 9.23; Found: C, 70.29; H, 9.11.

 

 

Received: March 17, 2005
Published on the web: April 29, 2005

 

 

* e-mail: alcindo@iq.usp.br
FAPESP helped in meeting the publication costs of this article.

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