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Arylsilanes as Precursors of Cyclohexa-2,5-dienylsilanes
ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5DIENYLSILANES
1
Y. Landais University of Bordeaux, Institute of Molecular Sciences, Talence, France
CHAPTER OUTLINE Preparation of cyclohexa-2,5-dienyldimethylsilanol
References
2
4
The Birch reduction of arenes is a well-known method to access functionalized cyclohexadienes using lithium, sodium, or potassium in ammonia as a reducing medium (1). This process has been applied to a large number of arenes and polyarenes, including aromatic compounds substituted with a silicon group (2). Eaborn first applied the Birch reduction to simple trialkylarylsilanes, obtaining the desired silyl-substituted cyclohexa-2,5-dienes (3,4). We extended to arylchlorosilanes this Birch reduction (5). The resulting silanol, which is obtained, may be manipulated further, for instance, through the formation of a siloxane, allowing further intramolecular hydrosilylation (6) or may be oxidized into a hydroxy group following the TamaoeKumadaeFleming process (7e9). The method can be extended to other chlorosilanes, but steric hindrance around the silicon center is detrimental to the yield in silanol. Preparation of such silyl-substituted cyclohexa-2,5-dienes may also be carried out as described by Woerpel through the metallation of the parent cyclohexa-2,5-diene with t-BuLi followed by the silylation of the resulting pentadienyl anion with the suitable chlorosilane (10). We have also developed an alternative electrochemical method (vide infra) using a sacrificial aluminum anode (4,5,11).
Efficient Methods for Preparing Silicon Compounds. http://dx.doi.org/10.1016/B978-0-12-803530-6.00001-9 Copyright © 2016 Elsevier Inc. All rights reserved.
1
2
Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
Preparation of cyclohexa-2,5-dienyldimethylsilanol Apparatus A dry 250-mL three-necked flask equipped with a magnetic stirrer, an inlet for argon, a low-temperature thermometer, a gas condenser cooled with liquid nitrogen, safety glasses, laboratory coat, and protective gloves. Chemicals Ammonia gas cylinder, lithium powder. PhMe2SiCl is commercially available but may also be prepared on 200e300 g scale from bromobenzene and Me2SiCl2 (12). Experimental procedure In a dry 250-mL three-necked flask, equipped with a magnetic stirrer, an inlet for argon, and a thermometer, was condensed NH3 (80 mL) at 80 C under argon. The phenyldimethylchlorosilane (1 mL, 6 mmol) was then slowly added and a white precipitate appeared. After 5 min, lithium powder (0.3 g, 42 mmol) was introduced and the solution turned immediately blue. This solution was then stirred at 80 C for 45 min and anhydrous NH4Cl was added until the blue coloration disappears. Ether (30 mL) and water (20 mL) were then added successively and ammonia was evaporated at room temperature. The aqueous layer was extracted with ether. The combined extracts were washed with water (2) then with a saturated NaCl solution, dried over MgSO4, and the solvents were evaporated in vacuo. The residue was then purified by Kugelrohr distillation (70 C, 0.4 mbar) or by flash chromatography through Florisil (petroleum ether/ EtOAc 95:5) to give the cyclohexadienylsilanol as a colorless oil (0.72 g, 77%).
Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
Apparatus A 100-mL one-compartment cell fitted with a sacrificial anode of aluminum and a cylindrical stainless grid. Chemicals LiCl, t-BuOH, hexamethylphosphoramide (HMPA). Attention! This experiment can only be done in a well-ventilated hood as HMPA is known as a carcinogenic solvent. Experimental procedure In a one-compartment cell fitted with a sacrificial anode of aluminum and a cylindrical stainless grid, was introduced under nitrogen, the supporting electrolyte LiCl (3.53 g, 83.3 mmol), t-BuOH (6 mL, 62.3 mmol), anhydrous THF (90 mL), HMPA (15 mL), and the t-butyldimethylphenylsilane (4 g, 20.8 mmol). Electrolysis (constant current 0.1 A) was then initiated and was maintained until the starting material has disappeared (z17 h) (monitored by GC). A solution of HCl 10% (50 mL) and pentane (30 mL) was then added to the reaction mixture and the organic layer was decanted. The aqueous layer was extracted with pentane (3 20 mL) and the combined extracts were washed with brine, dried over MgSO4, and the solvents were evaporated in vacuo to afford the silylcyclohexadiene as a colorless oil used in the next step without further purifications (3.5 g, 87%). 1 H NMR d (ppm) 5.78e5.50 (4H, m), 2.68 (2H, m), 2.40 (1H, m), 0.93 (s, 9H), 0.00 (6H, s); IR (film) 3028 cm1. Anal. Calcd for C12H22Si: C 74.17, H 11.42, Si 14.41. Found: C 74.20, H 11.48, Si 14.32. Application These dienes have been used in desymmetrization processes, for instance, using Sharpless enantioselective dihydroxylation (13) and aminohydroxylation reactions (14,15), methods affording the corresponding 1,2-diols or 1,2-amino alcohols with complete diastereocontrol, high level of regiocontrol, and moderate level of enantioselectivity (5e16). These intermediates were then further elaborated into a series of sugar mimics having potent glycosidase inhibitory activities (16). Woerpel has reported the functionalization of such silyl-substituted cyclohexadienes through a [3þ2] reaction with a chlorosulfonylisocyanate, leading after a few steps to an efficient synthesis of peduncularine (10).
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Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
References 1. Rabideau, P. W.; Marcinow, Z. Org. React. 1992, 42, 1. 2. Taber, D. F.; Bhamidipati, R. S.; Yet, L. J. Org. Chem. 1995, 60, 5537. 3. Eaborn, C.; Jackson, R. A.; Pearce, R. J. Chem. Soc., Perkin Trans. 1975, 1, 470. 4. Eaborn, C.; Jackson, R. A.; Pearce, R. J. Chem. Soc., Perkin Trans. 1974, 1, 2055. 5. Angelaud, R.; Landais, Y. J. Org. Chem. 1996, 61, 5202. 6. Angelaud, R.; Babot, O.; Charvat, T.; Landais, Y. J. Org. Chem. 1999, 64, 9613. 7. Fleming, I. Chemtracts, Org. Chem. 1996, 9, 1. 8. Jones, G. R.; Landais, Y. Tetrahedron 1996, 52, 7599. 9. Tamao, K. Adv. Silicon Chem. 1996, 3, 1. 10. Roberson, C. W.; Woerpel, K. A. Org. Lett. 2000, 2, 621. ger-Lambert, M.-P.; Dunoguès, J. J. Org. 11. Bordeau, M.; Biran, C.; Pons, P.; Le Chem. 1992, 57, 4705. 12. Andrianov, K. A.; Delazari, N. V. Doklady Akad. Nauk. SSSR 1958, 122, 393 (Chem. Abst. 1959, 53, 2133). 13. Kolb, H. C.; van Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483. 14. O’Brien, P. Angew. Chem. Int. Ed. Engl 1999, 38, 326. 15. Reddy, K. L.; Sharpless, K. B. J. Am. Chem. Soc. 1998, 120, 1207. 16. Abd Rahman, N.; Landais, Y. Curr. Org. Chem. 2002, 6, 1369.
1
Y. Landais University of Bordeaux, Institute of Molecular Sciences, Talence, France
CHAPTER OUTLINE Preparation of cyclohexa-2,5-dienyldimethylsilanol
References
2
4
The Birch reduction of arenes is a well-known method to access functionalized cyclohexadienes using lithium, sodium, or potassium in ammonia as a reducing medium (1). This process has been applied to a large number of arenes and polyarenes, including aromatic compounds substituted with a silicon group (2). Eaborn first applied the Birch reduction to simple trialkylarylsilanes, obtaining the desired silyl-substituted cyclohexa-2,5-dienes (3,4). We extended to arylchlorosilanes this Birch reduction (5). The resulting silanol, which is obtained, may be manipulated further, for instance, through the formation of a siloxane, allowing further intramolecular hydrosilylation (6) or may be oxidized into a hydroxy group following the TamaoeKumadaeFleming process (7e9). The method can be extended to other chlorosilanes, but steric hindrance around the silicon center is detrimental to the yield in silanol. Preparation of such silyl-substituted cyclohexa-2,5-dienes may also be carried out as described by Woerpel through the metallation of the parent cyclohexa-2,5-diene with t-BuLi followed by the silylation of the resulting pentadienyl anion with the suitable chlorosilane (10). We have also developed an alternative electrochemical method (vide infra) using a sacrificial aluminum anode (4,5,11).
Efficient Methods for Preparing Silicon Compounds. http://dx.doi.org/10.1016/B978-0-12-803530-6.00001-9 Copyright © 2016 Elsevier Inc. All rights reserved.
1
2
Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
Preparation of cyclohexa-2,5-dienyldimethylsilanol Apparatus A dry 250-mL three-necked flask equipped with a magnetic stirrer, an inlet for argon, a low-temperature thermometer, a gas condenser cooled with liquid nitrogen, safety glasses, laboratory coat, and protective gloves. Chemicals Ammonia gas cylinder, lithium powder. PhMe2SiCl is commercially available but may also be prepared on 200e300 g scale from bromobenzene and Me2SiCl2 (12). Experimental procedure In a dry 250-mL three-necked flask, equipped with a magnetic stirrer, an inlet for argon, and a thermometer, was condensed NH3 (80 mL) at 80 C under argon. The phenyldimethylchlorosilane (1 mL, 6 mmol) was then slowly added and a white precipitate appeared. After 5 min, lithium powder (0.3 g, 42 mmol) was introduced and the solution turned immediately blue. This solution was then stirred at 80 C for 45 min and anhydrous NH4Cl was added until the blue coloration disappears. Ether (30 mL) and water (20 mL) were then added successively and ammonia was evaporated at room temperature. The aqueous layer was extracted with ether. The combined extracts were washed with water (2) then with a saturated NaCl solution, dried over MgSO4, and the solvents were evaporated in vacuo. The residue was then purified by Kugelrohr distillation (70 C, 0.4 mbar) or by flash chromatography through Florisil (petroleum ether/ EtOAc 95:5) to give the cyclohexadienylsilanol as a colorless oil (0.72 g, 77%).
Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
Apparatus A 100-mL one-compartment cell fitted with a sacrificial anode of aluminum and a cylindrical stainless grid. Chemicals LiCl, t-BuOH, hexamethylphosphoramide (HMPA). Attention! This experiment can only be done in a well-ventilated hood as HMPA is known as a carcinogenic solvent. Experimental procedure In a one-compartment cell fitted with a sacrificial anode of aluminum and a cylindrical stainless grid, was introduced under nitrogen, the supporting electrolyte LiCl (3.53 g, 83.3 mmol), t-BuOH (6 mL, 62.3 mmol), anhydrous THF (90 mL), HMPA (15 mL), and the t-butyldimethylphenylsilane (4 g, 20.8 mmol). Electrolysis (constant current 0.1 A) was then initiated and was maintained until the starting material has disappeared (z17 h) (monitored by GC). A solution of HCl 10% (50 mL) and pentane (30 mL) was then added to the reaction mixture and the organic layer was decanted. The aqueous layer was extracted with pentane (3 20 mL) and the combined extracts were washed with brine, dried over MgSO4, and the solvents were evaporated in vacuo to afford the silylcyclohexadiene as a colorless oil used in the next step without further purifications (3.5 g, 87%). 1 H NMR d (ppm) 5.78e5.50 (4H, m), 2.68 (2H, m), 2.40 (1H, m), 0.93 (s, 9H), 0.00 (6H, s); IR (film) 3028 cm1. Anal. Calcd for C12H22Si: C 74.17, H 11.42, Si 14.41. Found: C 74.20, H 11.48, Si 14.32. Application These dienes have been used in desymmetrization processes, for instance, using Sharpless enantioselective dihydroxylation (13) and aminohydroxylation reactions (14,15), methods affording the corresponding 1,2-diols or 1,2-amino alcohols with complete diastereocontrol, high level of regiocontrol, and moderate level of enantioselectivity (5e16). These intermediates were then further elaborated into a series of sugar mimics having potent glycosidase inhibitory activities (16). Woerpel has reported the functionalization of such silyl-substituted cyclohexadienes through a [3þ2] reaction with a chlorosulfonylisocyanate, leading after a few steps to an efficient synthesis of peduncularine (10).
3
4
Chapter 1 ARYLSILANES AS PRECURSORS OF CYCLOHEXA-2,5-DIENYLSILANES
References 1. Rabideau, P. W.; Marcinow, Z. Org. React. 1992, 42, 1. 2. Taber, D. F.; Bhamidipati, R. S.; Yet, L. J. Org. Chem. 1995, 60, 5537. 3. Eaborn, C.; Jackson, R. A.; Pearce, R. J. Chem. Soc., Perkin Trans. 1975, 1, 470. 4. Eaborn, C.; Jackson, R. A.; Pearce, R. J. Chem. Soc., Perkin Trans. 1974, 1, 2055. 5. Angelaud, R.; Landais, Y. J. Org. Chem. 1996, 61, 5202. 6. Angelaud, R.; Babot, O.; Charvat, T.; Landais, Y. J. Org. Chem. 1999, 64, 9613. 7. Fleming, I. Chemtracts, Org. Chem. 1996, 9, 1. 8. Jones, G. R.; Landais, Y. Tetrahedron 1996, 52, 7599. 9. Tamao, K. Adv. Silicon Chem. 1996, 3, 1. 10. Roberson, C. W.; Woerpel, K. A. Org. Lett. 2000, 2, 621. ger-Lambert, M.-P.; Dunoguès, J. J. Org. 11. Bordeau, M.; Biran, C.; Pons, P.; Le Chem. 1992, 57, 4705. 12. Andrianov, K. A.; Delazari, N. V. Doklady Akad. Nauk. SSSR 1958, 122, 393 (Chem. Abst. 1959, 53, 2133). 13. Kolb, H. C.; van Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483. 14. O’Brien, P. Angew. Chem. Int. Ed. Engl 1999, 38, 326. 15. Reddy, K. L.; Sharpless, K. B. J. Am. Chem. Soc. 1998, 120, 1207. 16. Abd Rahman, N.; Landais, Y. Curr. Org. Chem. 2002, 6, 1369.