Efficient Condensation of Cycloketones and Acetone Using SOCl₂/EtOH

SOCl₂/EtOH을 이용한 사이클로케톤과 아세톤의 효율적인 응축반응

INTRODUCTION

2-(1-Cyclohexenyl)-cyclohexanone (1) (Scheme 1) is an important intermediate for the synthesis of OPP (o-C6H5C6H4OH) which is used as antiseptic. Both 1 and bicyclopentyliden-2-one (2) (Scheme 1) are original materials for the synthesis of some unsymmetrical trisannelated benzenes (4) and (5)1 (Scheme 3). 4-Methyl-3-penten-2-one (3) (Scheme 2) is a common solvent for some colophony and fibrin, an important intermediate of some drugs and pesticides.

Cyclohexanone has long been known to undergo self-condensation to 1.2 The condensation can be catalyzed by acids, bases, or by heat alone. A few methods, for instance, using tetraalkoxysilane in the presence of fluoride ions,3 RuCl3,4 CuCl2 1,5 as catalyst have been reported for the synthesis of 1 and 2, and several methods have been described for the preparation of 3.4,6 The literature synthetic methods involve some disadvantageous reaction conditions such as too high or too low temperature, high pressure and long reaction time.

Scheme 1.

Scheme 2.

Scheme 3.

 

RESULT AND DISSCUSSSION

On the basis of our previous reports the synthesis of 1, 3, 5-triarylbenzene,7 asymmetrical 1, 3, 5-triarylbenzene, 8 chalcones9 and α, α'-bis(substituted benzylidene) ketones10 catalyzed by SOCl2/EtOH, we expanded this method to the synthesis of symmetric trisannelated benzenes and 1, 3, 5-trimethyl benzene. During the study of synthesizing the symmetrical trisannelated benzenes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12-dodecahydro-triphenylene (6) and 2, 3, 4, 5, 6, 7, 8, 9-octahydro-1H-trindene (7) (Scheme 4), we noticed that oil with high boiling point could be obtained as the main product (see the synthesis of compouds 1 and 2) if the amount of SOCl2 was reduced and the reaction time was prolonged. The oil was isolated by distillation and characterized by GC-mass and 1H NMR, and the analytical data showed that it was the intermediate of the triple condensation reaction. We optimized the reaction conditions and found that SOCl2/EtOH reagent is also a good catalyst for synthesizing the dimers of these ketones.

Scheme 4.

Furthermore, we found that the alcohol serving as reaction solvent was indispensable for the catalyst system. Other solvents such as toluene and pyridine were not efficient for the reaction, only alcohols catalysed the condensation reaction. There is no significant variation of yields between anhydrous CH3OH and anhydrous C2H5OH. On the basis of these results, we think the reaction proceeds via the reaction of the enol sulfite ester of the ketones, and the byproduct HCl may accelerate the reaction.7,9,10 The detailed mechanistic investigation and further applications of this reaction are under study in our laboratory.

 

CONCLUSION

In this paper, an efficient and simple method for the synthesis of the dimers of cycloketones and acetone in the presence of thionyl chloride in anhydrous ethanol has been reported. Comparing with other methods, this method is easily available with cheap catalyst, simple manipulation under mild conditions. We believe this reaction will expand the application of the thionyl chloride in organic synthesis.

 

EXPERIMENTAL

Melting points were determined on the kofler micro melting point apparatus without correction. Infrared spectra were recorded on a PTS-40 IR spectrophotometer in KBr. 1H NMR spectra were measured in CDCl3 using TMS as internal standard on a BRUKER 80 MHz NMR spectrometer. The mass spectra were performed on an Agilent GC-MS spectrometer.

Synthesis of 2-(1-cyclohexenyl)-cyclohexanone (1):

To a stirred mixture of cyclohexanone (15.54 mL, 0.15 mol; freshly distilled) and anhydrous ethanol (43.7 mL, 0.75 mol), thionyl chloride (7.28 mL, 0.1 mol) was added dropwise. The mixture was stirred for 24 hours, saturated aqueous Na2CO3 solution was added. The mixture was extracted with ethyl ether (20 mL) three times, and the combined solution was dried over anhydrous MgSO4. After evaporation of the volatiles on a rotaevaporator, the residue was distilled at reduced pressure (140-142℃/13 mmHg), total yield: 60%. b.p.: 140-142℃/13tor. (lit.3: 142℃ /13tor.); IR (KBr, cm-1): 2930, 2870, 1717, 1450, 920, 830; 1H NMR (CDCl3, ppm): 1.9-2.4(m, 16H), 2.9(m, 1H), 5.5(m, 1H); Mass(m/z, %): 178(M+, 60), 149(100).

Synthesis of bicyclopentyliden-2-one (2):

To a stirred mixture of cyclopentanone (13.27 mL, 0.15 mol; freshly distilled) and anhydrous ethanol (43.7 mL, 0.75 mol), thionyl chloride (1.82 mL, 0.025 mol) was added dropwise. In a similar experiment as described for 1, the residue was distilled at reduced pressure (120-122℃/12mmHg), total yield: 55%. b.p.: 120-122℃/12tor. (lit.4: 120-124℃ /12tor.); IR (KBr, cm-1): 2950, 2850, 1700, 1445, 1120; 1H NMR (CDCl3, ppm): 1.9-2.3(m, 12H), 2.8(m, 1H), 5.5(m, 1H); Mass (m/z, %): 150 (M+, 55), 121(100).

Synthesis of 4-methyl-3-penten-2-one (3):

To a stirred mixture of acetone (11 mL, 0.15 mol) and anhydrous ethanol (35 mL, 0.6 mol), thionyl chloride (3.64 mL, 0.05 mol) was added dropwise. In a similar experiment as described for 1, the residue was purified by column chromatography on silica gel using cyclohexane / EtOAc (10/1, v/v) as eluent, isolated yield: 40%. lit.,11 IR (KBr, cm-1): 2990, 2910, 1690, 1620, 1440, 1350, 1210, 1160, 960, 620; 1H NMR(CDCl3, ppm): 1.9(s, 3H), 2.2(s, 6H), 6.1(s, 1H); Mass: (m/z, %): 98 (M+, 53), 83(100).

Synthesis of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12-dodecahydrotriphenylene(DTP)(6):

To a stirred mixture of cyclohexanone (15.54 mL, 0.15 mol, freshly distilled) and anhydrous ethanol (43.7 mL, 0.75 mol), thionyl chloride (14.56 mL, 0.2 mol) was added dropwise, the mixture was refluxed for 2 hours. Then saturated aqueous Na2CO3 solution was added and the mixture was extracted with ethyl ether (20 mL) twice, and finally dried over anhydrous MgSO4. After evaporation of the volatiles, the residue was purified by column chromatography on silica gel using petroleum ether as eluent, isolated yield: 60%. m.p.: 229℃ (lit12. 230℃); IR(KBr, cm-1): 2920, 2850, 1445, 1420; 1H NMR (CDCl3, ppm): 1.7 (s, 12H), 2.5(s, 12H); Mass (m/z, %): 240(M+,100).

Synthesis of 2, 3, 4, 5, 6, 7, 8, 9-octahydro-1Htrindene(7)

The similar synthetic procedure was applied as described for 6 (taking cyclopentanone as the starting material). The residue was purified by column chromatography on silica gel using petroleum ether as eluent, isolated yield: 52%. m.p.: 95℃ (lit13.97.5 ℃); IR(KBr, cm-1): 2837, 1448, 1424, 1300, 1275; 1H NMR (CDCl3, ppm): 2.7(t,12H, J=7.3Hz), 1.9-2.4(m, 6H); Mass (m/z, %): 198(M+,100).