Short communication
Diels-Alder Reactions of Styrylcyclohexenones: an Efficient Procedure for the Synthesis of Substituted Dehydrodecaline Derivatives
M. Saeed Abaee,1* Mohammad M. Mojtahedi,1* M. Taghi Rezaei2
and Hamid Reza Khavasi3
1 Chemistry and Chemical Engineering Research Center of Iran, P.O.Box 14335-186, Tehran, Iran
2 Chemistry Department, Islamic Azad University, Saveh Branch, Saveh, Iran
3 Department of Chemistry, Shahid Beheshti University, G. C., Evin, Tehran 1983963113, Iran
* Corresponding author: E-mail: mojtahedi@ccerci.ac.ir; abaee@ccerci.ac.ir Fax: +9821-44580762
Received: 22-12-2010
Abstract
The Diels-Alder reaction of styrylcyclohex-2-enone derivatives 1 with N-phenylmaleimide was shown to be an efficient pathway for the synthesis of substituted dehydrodecaline derivatives. At elevated temperatures, mixtures of endo/exo adducts were formed, while in the presence of TiCl4 exclusive formation of the endo stereoisomer was observed. Spectroscopic analysis and X-ray crystallography confirmed the formation of the endo adducts.
Keywords: Styrylcyclohexenone dienes, Diels-Alder reaction, Lewis acid catalysis, dehydrodecalines, cycloaddition
1. Introduction
The Diels-Alder (DA) cycloaddition1 is considered to be one of the key reactions in synthetic organic chemistry2 due to its ability to simultaneously yield two carbon-carbon bonds, a six-membered ring, and up to four stereogenic centers with predictable stereoselectivity in a single step reaction.3 The reactivity and selectivity features of DA cycloadditions have been enhanced significantly in recent years with the use of chiral Lewis acids,4 self-assembling reactants,5 enantioselective catalysts,6 and transiently tethered trienes.7 Further enhancement is also achieved by the application of intramolecular and transannular DA reactions of appropriate trienes in the synthesis of complex multicyclic8 and natural product9 molecules.
The dehydrodecaline skeleton constitutes a structural fraction of several natural products and industrially significant perfumes.10 In the framework of our investigations on Lewis acid catalyzed carbonyl group chemistry,11 we recently reported the synthesis of novel styrylcyclo-hex-2-enone derivatives 112 which could be explored for
their DA reactivity. Through the positive results, we were encouraged to investigate the cycloaddition reactions of precursors of type 1 to examine their potential for assembling dehydrodecaline systems. Hereby, we report the synthesis and structural elucidation of the novel products obtained from the [4+2] cycloadditions of 1 with N-phenylmaleimide (NPM) under both thermal and TiCl4-mediated conditions (Scheme 1).
Scheme 1
2. Results and Discussion
Initially, we attempted thermal cycloaddition of 1a with NPM (Table 1). A 1:1 solution of the diene and the
dienophile in refluxing toluene completely converted to [4+2] cycloadducts within 10 hours. NMR analysis of the reaction mixture suggested formation of both adducts in a 9:1 ratio (entry 1). The structure of the major product, 2a, isolated by column chromatography, was assigned as endo in which the newly formed n bond had rearranged to the more stable tetrasubstituted enone position. The stere-ochemical assignment was based on the 1H NMR signal at the position 3a which splits the proton 4 to exhibit a medium coupling constant of about 7 Hz (Figure 1). This coupling constant is in accordance with the endo structure as
Table 1: Thermal DA reactions of 1a-g with NPM.
opposed to the exo stereoisomer, which is expected to exhibit a large 3JH,H for the same proton.
exo
endo
Figure 1. Diagnostic H-H coupling constants of adducts. For simplicity, only two hydrogen atoms at C3a and C4 are shown.
Entry
Diene
Major product
Endo/Exoa Yield (%)b
C^ ,Ptl
la
2a
9:1
92
1b
2b
9:1
88
'OMe
OMe
lc
2c
9:1
91
Id
2d
8:2
87
1e
2e
7:3
86
1f
7:3
91
lg
2g
9:1
92
a Determined by 'H NMR analysis of the crude mixtures. b Isolated yields.
1
2
3
4
5
6
7
Next, we examined the DA reactions of some other dienes (1b-g) with NPM. As a result, formation of endo-2b-g derivatives was observed as the major products in the reaction mixtures (Table 2, entries 2-7). In all cases endo products were isolated by column chromatography and their structures were assigned in the same way by spectroscopic methods, as described for endo-2a. In order to verify the structure of the stereoadducts, a single crystal of en-do-2c was prepared and analyzed by X-ray crystallography. The result, depicted in Figure 2, clearly indicates the formation of endo stereoisomer as the major DA adduct.
Figure 2. Crystal structure of endo-2c. Displacement ellipsoids are at 50% probability level.
Due to usually observed rate and selectivity enhancements associated with Lewis acid (LA) mediated DA cycloadditions,13 we next examined the use of various Lewis acids (LiClO4, MgBr2.OEt2, SnCl4, and TiCl4) to boost the DA reactions of 1 with NPM. The best conditions were ob-
tained when TiCl4 was used and endo adducts were the sole products within 1 hour of reaction (Table 2).
Table 2: Endo selective TiCl4-mediated DA reactions of 1a-g with NPM.
Entry	Diene	Product	Yield (%)a
1	1a	2a	92
2	1b	2b	90
1	1c	2c	95
4	1d	2d	89
5	1e	2e	90
6	1f	2f	93
7	1g	2g	95
a Isolated yields of endo adducts
As shown in Table 2, the LA-catalyzed reactions proceed much faster than the corresponding thermal reac-
tions, which is usually observed for DA cycloadditions mediated with Lewis acids.13 The exclusive high yield formation of the endo adducts can be attributed to the TiCL4-mediated catalysis of the process which is already observed for similar [4+2] reactions with NPM as dienophile.2
3. Experimental
3. 1. General
The progress of the reactions was monitored by TLC using silica-gel coated plates (stationary phase) and ethyl acetate/hexane solution (1:2, mobile phase). Melting points are uncorrected. FT-IR spectra were recorded using KBr disks on a Bruker Vector-22 IR spectrometer. 1H and 13C NMR spectra were obtained on a FT-NMR Bruker Ultra Shield™ (500 MHz) instrument as CDCl3 solutions. Chemical shifts are expressed relative to the Me4Si as the internal standard.
Mass spectra were obtained using a Finnigan Mat 8430 apparatus operating with an ionization potential of 70 eV. Elemental analyses were performed using a Thermo Finnigan Flash EA 1112 instrument. Dienes 1a-d and 1g were synthesized as reported in our recent work12 and a similar procedure was used for the synthesis of the two new dienes (1e and 1f). All other reagents were purchased from commercial sources and were used fresh after being purified by standard procedures.
3. 2. Typical Procedure for Thermal DA Reactions
A solution of a diene (2 mmol) and NPM (363 mg, 2.1 mmol) in toluene (2 mL) was refluxed for 8-10 hours in an atmosphere of argon. When TLC showed completion of the reaction, the mixture was cooled to room temperature and concentrated under vacuum. The endo-2a-g was obtained by column chromatography of the residues over silica-gel using EtOAc/hexane solution (1:2).
3. 3. Typical Procedure for TiCl4 Mediated DA Reactions
A mixture of a diene (2 mmol), NPM (363 mg, 2.1 mmol), and TiCl4 (110 pL, 1 mmol) in CH2Cl2 (4 mL) was stirred at room temperature for about 1 hour in an inert atmosphere of argon. When TLC showed completion of the reaction, the mixture was diluted with CH2Cl2 (10 mL) and washed with saturated aqueous solution of NaHCO3 (2 x 10 mL). Organic layer was passed through a short column of Na2SO4 and concentrated under vacuum. The endo-2a-g were obtained by column chromatography of the residues over silica-gel using EtOAc/hexane solution (1:2).
3. 4. Spectral Data of New Compounds
(£)-3-(3-Bromostyryl)-5,5-dimethylcyclohex-2-enone
(1e). IR (KBr) v 3025, 1643 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.65 (s, 1H), 7.46-7.42 (m, 2H), 7.25 (dd, J= 7.9 and 7.8 Hz, 1H), 6.92 (s, 2H), 6.11 (s, 1H), 2.48 (s, 2H), 2.34 (s, 2H), 1.13 (s, 6H); 13C NMR (CDCl3, 125 MHz) 5 200.5, 154.4, 138.6, 133.6, 132.2, 131.4, 130.8, 130.4, 128.3, 126.2, 51.8, 39.5, 33.8, 28.9; MS (70 eV) m/z: 304 (M+), 286, 141, 115. Calcd. for C16H17BrO: C 62.96, H 5.61. Found: C 63.02, H 5.63.
(£)-5,5-Dimethyl-3-(2-(naphthalen-2-yl)vinyl)cyclo-hex-2-enone (1f). Mp = 114-115 °C; IR (KBr) v 1648, 1605, 1300 cm-1; 1H NMR (CDCl3, 500 MHz) 5 8.19 (d, J = 8.2 Hz, 1H), 7.91 (d, J = 7.2 Hz, 1H), 7.88 (d, J = 8.2 Hz, 1H), 7.82 (d, J = 15.9 Hz), 7.77 (d, 1H, J = 7.2 Hz), 7.63-7.50 (m, 3H), 7.00 (d, J = 15.9 Hz, 1H), 6.17 (s, 1H), 2.62 (s, 2H), 2.38 (s, 2H), 1.20 (s, 6H); 13C NMR (CDCl3, 125 MHz) 5 200.6, 155.2, 134.2, 133.8, 132.8, 132.1, 131.7, 129.9, 129.3, 127.8, 127.0, 126.5, 126.1, 124.7,
123.7,	51.9, 39.7, 33.8, 29.0; MS (70 eV) m/z: 276 (M+), 191, 165, 152. Calcd. for C20H20O: C 86.92, H 7.29.
Found: C 86.59, H 7.28.	20 20
(3aS,4S,9£S)-7,7-Dimethyl-2,4-diphenyl-4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9(2H,3aH)-trione
(endo-2a). White crystals were obtained in 92% yield. Mp = 114-116 °C; IR (KBr) v 1716, 1670, 1380 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.44-7.27 (m, 7H), 7.23-7.17 (m, 2H), 6.643 (d, J = 7. 5 Hz, 1H), 4.45 (d, J = 7.8 Hz, 1H), 3.63-3.60 (m, 1H), 3.55 (dd, J = 7.8, 7 Hz, 1H), 2.76 (dd, J = 18.5, 4.8 Hz, 1H), 2.68-2.63 (m, 2H), 2.52 (d, J = 18.2 Hz, 1H), 2.42 (d, J = 15.8 Hz, 1H), 2.35 (d, J = 18.2 Hz, 1H), 1.21 (s, 3H), 1.11 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 196.9, 176.2, 174.1, 156.9, 140.3, 131.8, 129.2, 129.1, 128.7, 128.1, 126.7, 126.5, 51.7, 46.2, 44.8, 39.4, 38.6, 35.8, 33.9, 29.3, 28.2; MS (70 eV) m/z: 399 (M+), 274, 196, 167, 141, 91, 43. Calcd. for C26H25NO3: C 78.17, H 6.31. Found: C 78.35, H 6.13.
(3aS,4S,9£S)-7,7-Dimethyl-2-phenyl-4-(p-tolyl)-4,5,6, 7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9(2H, 3aH)-trione (endo-2b). White crystals were obtained in 90% yield. Mp = 120-122 °C; IR (KBr) v 1716, 1668, 1378 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.33-7.18 (m, 3H), 7.10 (s, 4H), 6.65-6.633 (m, 2H), 4.42 (d, J = 8 Hz, 1H), 3.58-3.56 (m, 1H), 3.51 (dd, J = 8 and 6.7 Hz, 1H), 2.74 (dd, J = 18.5, 5.1 Hz, 1H), 2.66-2.59 (m, 2H), 2.49 (d, J = 16 Hz, 1H), 2.43 (d, J = 16 Hz, 1H), 2.33 (s, 3H), 2.20 (d, J = 16 Hz, 1H), 1.20 (s, 3H), 1.11 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 196.8, 176.3, 174.1, 156.8,
137.8,	137.1, 134.6, 131.9, 129.8, 129.1, 128.5, 126.7, 126.5, 51.7, 46.2, 44.8, 39.1, 38.5, 36.0, 33.9, 29.3, 28.2, 21.4; MS (70 eV) m/z: 413 (M+), 210, 167, 105, 91, 43. Calcd. for C27H27NO3: C 78.42, H 6.58. Found: C 78.83, H 6.50.
(3«S,4S,96S)-4-(4-Methoxyphenyl)-7,7-dimethyl-2-phenyl-4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9(2H,3aH)-trione (endo-2c). White crystals were obtained in 95% yield. Mp = 196-197 °C; IR (KBr) v 1714, 1668, 1380 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.32-7.26 (m, 3H), 7.14 (d, J =7.8 Hz, 2H), 6.84 (d, J =7.8 Hz, 2H), 6.71-6.68 (m, 2H), 4.42 (d, J = 7.9 Hz, 1H), 3.79 (s, 3H), 3.61-3.58 (m, 1H), 3.52 (dd, J = 8, 6.5 Hz, 1H), 2.76 (dd, J = 18.7, 5.1 Hz, 1H), 2.67 (d, J = 15.7 Hz, 1H), 2.62 (dd, J = 18.7, 4.2 Hz, 1H), 2.52 (d, J = 18.2 Hz, 1H), 2.42 (d, J = 15.7 Hz, 1H), 2.35 (d, J = 18.2 Hz, 1H), 1.22 (s, 3H), 1.12 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 198.3, 177.9, 175.5, 161.0, 158.2, 133.5, 133.3, 131.2, 130.5, 130.1, 128.1, 128.0, 116.0, 57.2, 53.2, 47.7, 46.3,
40.1,	39.9, 37.6, 35.4, 30.9, 29.6; MS (70 eV) m/z: 429 (M+), 281, 226, 121. Calcd. for C27H27NO4: C 75.50, H 6.34. Found: C 75.34, H 6.27.
(3«S,4S,96S)-4-(4-Chlorophenyl)-7,7-dimethyl-2-phe nyl-4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9 (2H,3aH)-trione (endo-2d). White crystals were obtained in 89% yield. Mp = 209-211 °C; IR (KBr) v 1713, 1659, 1380 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.36-7.33 (m, 3H), 7.31 (d, J = 8.5 Hz, 2H), 7.18 (d, J = 8.5 Hz, 2H), 6.77-6.75 (m, 2H), 4.50 (d, J = 7.2 Hz, 1H), 3.58-3.54 (m, 2H), 2.72 (dd, J = 18 and 4.2 Hz, 1H), 2.67-2.64 (m, 2H), 2.50 (d, J = 18 Hz, 1H), 2.42 (d, J = 16 Hz, 1H), 2.36 (d, J = 18 Hz, 1H), 1.21 (s, 3H), 1.13 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 196.7, 175.9, 173.9, 156.6, 138.6, 134.0, 131.7, 130.0, 129.3, 128.8, 126.9, 126.5, 51.6,
46.2,	47.7, 39.0, 38.7, 35.3, 33.8, 29.1, 28.4; MS (70 eV) m/z: 433 (M+), 230, 119, 91, 57. Calcd. for C26H24ClNO3: C 71.97, H 5.57. Found: C 71.58, H 5.61.
(3«S,4S,96S)-4-(3-Bromophenyl)-7,7-dimethyl-2-phe nyl-4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9 (2H,3aH)-trione (endo-2e). White crystals were obtained in 90% yield. Mp = 109-111°C; 1H NMR (CDCl3, 500 MHz) 5 7.44-7.43 (m, 2H), 7.37-7.29 (m, 3H), 7.21-7.16 (m, 2H), 6.88-6.86 (m, 2H), 4.51(d, J = 8.3 Hz, 1H), 3.59 (dd, J = 8.3 and 6.3 Hz, 1H), 3.49-3.47 (m, 1H), 2.68-2.66 (m, 2H), 2.61 (d, J = 16 Hz, 1H), 2.48 (d, J = 18.4 Hz, 1H), 2.43-2.36 (m, 2H), 1.19 (s, 3H), 1.12 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 196.7, 175.8, 173.9, 156.7, 142.5, 131.8, 131.1, 130.6, 129.3, 128.8, 127.1, 127.0, 126.5, 123.1, 51.6, 46.3, 44.8, 39.4, 39.1, 34.8, 33.7, 28.8, 28.7; MS (70 eV) m/z: 477 (M+), 274, 165, 152, 119. Calcd. for C26H24BrNO3: C 65.28, H 5.06. Found: C 65.67, H 4.70.
(3«S,4S,96S)-7,7-DimethyM-(naphthalen-2-yl)-2-phe nyl-4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9 (2H,3aH)-trione (endo-2f). White crystals were obtained in 93% yield. Mp = 139-140 °C; IR (KBr) v 1716, 1663, 1375 cm-1; 1H NMR (CDCl3, 500 MHz) 5 8.09 (d, J = 8.5 Hz, 1H), 7.95 (d, J = 8 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H),
7.62 (dd, J = 7.3 and 7.2 Hz, 1H), 7.56 (dd, J = 7.6 and 7.2 Hz, 1H), 7.48 (dd, J = 7.9 and 7.5 Hz, 1H), 7.42 (d, J = 7.2 Hz, 1H), 7.38-7.29 (m, 3H), 7.00 (d, J = 7.5 Hz, 2H), 4.77 (d, J = 8.7 Hz, 1H), 4.11-4.07 (m, 1H), 3.90-3.87 (m, 1H), 2.97 (dd, J = 17 and 11 Hz, 1H), 2.63-2.58 (m ,2H), 2.49-2.44 (m, 3H), 1.17 (s, 3H), 1.16 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 196.7, 175.3, 174.6, 158.9, 135.8, 134.3, 132.1, 131.5, 129.8, 129.3, 128.7, 128.5, 127.9, 126.9, 126.5, 126.1, 125.7, 125.4, 122.8, 51.5, 46.6, 44.0, 40.1, 36.4, 34.6, 33.6, 29.4, 28.0; MS (70eV) m/z: 449 (M+), 202, 152, 119, 91. Calcd. for C30H27NO3: C 80.15, H 6.05. Found: C 80.01, H 6.19.
Study of the reactions with singly activated dienophilic systems and attempts to perform intramolecular DA reactions are also underway.
5. Acknowledgement
Ms. Faraji is gratefully acknowledged for conducting the elemental analyses.
6. References
(3«fl,4S,96S)-7,7-Dimethyl-2-phenyM-(thiophen-2-yl) -4,5,6,7,8,9b-hexahydro-1H-benzo[e]isoindole-1,3,9 (2H,3aH)-trione (endo-2g). White crystals were obtained in 95% yield. Mp = 188-190 °C; IR (KBr) v 1716, 1668, 1384 cm-1; 1H NMR (CDCl3, 500 MHz) 5 7.32-7.26 (m, 3H), 7.18 (dd, J = 5.1 and 1 Hz, 1H), 6.94-6.92 (m, 1H), 6.90 (d, J = 3 Hz, 1H), 6.70-6.68 (m, 2H), 4.34 (dd, J = 8.3 and 1.8 Hz, 1H), 4.06-4.04 (m, 1H), 3.50 (dd, J = 8.3 and 6 Hz, 1H), 2.82 (dd, J = 18.5 and 4.2 Hz, 1H), 2.66 (d, J = 15.3 Hz, 1H), 2.58 (dd, J = 18.5 and 3 Hz, 1H), 2.51 (d, J = 18.3 Hz, 1H), 2.39 (d, J = 15.3 Hz, 1H), 2.28 (d, J = 18.3 Hz, 1H), 1.21 (s, 3H), 1.07 (s, 3H); 13C NMR (CDCl3, 125 MHz) 5 197.1, 176.2, 173.6, 154.6, 141.9, 131.9, 129.2, 127.8, 127.4, 127.3, 126.9, 126.8, 125.5, 51.9, 46.4, 45.0, 38.0, 37.5, 34.9, 34.0, 30.0, 27.8; MS (70 eV) m/z: 405 (M+), 257, 202, 119, 91. Calcd. for C24H23SNO3: C 71.09, H 5.72. Found: C 70.97, H 5.76.
3. 5. X-Ray Data for Endo-2c
C27H27NO4, M = 429.50 g/mol, triclinic system, space group) PI, a = 10.0376(9), b = 10.8919(9), c = 11.4595(10) A, a = 89.219(7), p = 65.236(7), y = 81.641(7)°, V = 1124.00(18) A3, Z = 2, Dc = 1.269 g cm-3, ^(Mo-Ka) = 0,085 mm-1, crystal dimension: 0.45 x 0.23 x 0.15 mm. The structure refinement and data reduction was carried out with SHELXL. The non-hydrogen atoms were refined anisotropically by full matrix least-squares on F2 values to final R1 = 0.0623, wR2 = 0.1300 and S = 1.128 with 292 parameters using 6027 independent reflections (8 range = 1.96-29.33°). Hydrogen atoms were located from expected geometry and were not refined. Crystallographic data for endo-2c have been deposited and could be obtained free of charge on application at the Cambridge Crystallographic Data Centre.
4. Conclusions
In summary, the DA reactions of 1 with NPM illustrated stereoselective formation of the corresponding endo adducts which could be appropriate precursors for the synthesis of other substituted dehydrodecaline derivatives.
1.	O. Diels, K. Alder, Justus Liebigs Ann. Chem. 1928, 460, 98-112.
2.	W. Oppolzer, in: Comprehensive Organic Synthesis, B. M. Trost (Ed.), Pergamon Press, New York, USA, 1991, Vol. 5, pp. 315-318.
3.	F. Fringuelli, A. Taticchi, The Diels-Alder Reaction: Selected Practical Methods, John Wiley & Sons, Chichester, England, 2002, pp. 1-25.
4.	a) J. Rickerby, M. Vallet, G. Bernardinelli, F. Viton, E. P. Kundig, Chem. -Eur. J. 2007, 13, 3354-3368. b) J. D. McGilvra, V. H. Rawai, Synlett 2004, 2440-2442.
5.	a) M. Yoshizawa, M. Tamura, M. Fujita, Science 2006, 312, 251-254. b) D. E. Ward, M. S. Abaee, Org. Lett. 2000, 2, 3937-3940. c) J. M. Kang, J. Santamaria, G. Hilmersson, J. Rebek, J. Am. Chem. Soc. 1998, 120, 7389-7390. d) J. M. Kang, J. Rebe, Nature 1997, 385, 50-52.
6.	a) A. J. Davenport, D. L. Davies, J. Fawcett, D. R. Russell, J. Chem. Soc., Dalton Trans. 2004, 1481-1492. b) C. Palomo, M. Oiarbide, J. M. Garcia, A. Gonzalez, E. Arceo, J. Am. Chem. Soc. 2003, 125, 13942-13943. c) A. M. Sarotti, R. A. Spanevello, A. G. Suarez, Tetrahedron 2009, 65, 3502-3508. d) M. Asano, M. Inoue, T. Katoh, Synlett 2005, 1539-1542.
7.	a) L. Fensterbank, M. Malacria, S. M. Sieburth, Synthesis 1997, 813-854. b) M. Bols, T. Skrydstrup, Chem. Rev. 1995, 95, 1253-1277.
8.	(a) K. M. Brummond, L. F. You, Tetrahedron 2005, 61, 6180-6185. b) C. C. Hsu, C. C. Lai, S. H. Chiu, Tetrahedron 2009, 65, 2824-2829. c) M. S. Souweha, G. D. Enright, A. G. Fallis, Org. Lett. 2007, 9, 5163-5166. d) L. F. You, R. P. Hsung, A. A. Bedermann, A. V. Kurdyumov, Y. Tang, G. S. Buchanan, K. P. Cole, Adv. Synth. Catal. 2008, 350, 28852891. e) M. Asano, M. Inoue, K. Watanabe, H. Abe, T. Katoh, J. Org. Chem. 2006, 71, 6942-6951.
9.	(a) P. Wessig, G. Muller, Chem. Rev. 2008, 108, 2051-2063. b) S. Born, G. Bacani, E. E. Olson, Y. Kobayashi, Synlett 2008, 2877-2881. c) M. G. Constantino, V. Aragao, G. V. J. da Silva, Tetrahedron Lett. 2008, 49, 1393-1395. d) C. K. Jana, A. Studer, Chem. Eur. J. 2008, 14, 6326-6328. e) S. Jimenez-Alonso, H. Chavez, A. Estevez-Braun, A. G. Ravelo, G. Feresin, A. Tapia, Tetrahedron 2008, 64, 8938-8942. f) S. M. Winbush, D. J. Mergott, W. R. Roush, J. Org. Chem. 2008, 73, 1818-1829. g) S. Phoenix, M. S. Reddy, P. Deslongchamps, J. Am. Chem. Soc. 2008,130, 13989-13995.
10.	M. Bella, M. Cianflone, G. Montemurro, P. Passacantilli, G. Piancatelli, Tetrahedron 2004, 60, 4821-4827.
11.	a) M. M. Mojtahedi, M. S. Abaee, T. Alishiri, Tetrahedron Lett. 2009, 50, 2322-2325. b) M. S. Abaee, M. M. Mojtahedi, V. Hamidi, A. W. Mesbah, W. Massa, Synthesis 2008, 2122-2126. c) M. M. Mojtahedi, E. Akbarzadeh, R. Sharifi, M. S. Abaee, Org. Lett. 2007, 9, 2791-2793. d) M. S. Abaee, M. M. Mojtahedi, M. M. Zahedi, R. Sharifi, H. Khavasi, Synthesis 2007, 3339-3344. e) M. M. Mojtahedi, M. S. Abaee, H. Abbasi, Can. J. Chem. 2006, 84, 429-432. f) M. S. Abaee, R. Sharifi, M. M. Mojtahedi, Org. Lett. 2005, 7, 5893-5895. g) M. S. Abaee, M. M. Mojtahedi, M. M. Zahedi, Synlett 2005, 2317-2320.
12.	M. M. Mojtahedi, M. S. Abaee, M. M. Zahedi, M. R. Jalali, A. W. Mesbah, W. Massa, R. Yaghoubi, M. Forouzani, Mo-natsh. Chem. 2008, 139, 917-921.
13.	a) A. Müller, A. Endres, G. Maas, Acta Chim. Slov. 2009, 56, 535-544. b) G. Bhargava, A. Anand, M. P. Mahajan, T. Saito, K. Sakai, C. Medhi, Tetrahedron 2008, 64, 6801-6808. c) G. Bhargava, M. P. Mahajan, T. Saito, T. Otani, M. Kurashima, K. Sakai, Eur. J. Org. Chem. 2005, 2397-2405. d) S. Rey-mond, J. Cossy, Chem. Rev. 2008, 108, 5359-5406. e) J. Safaei-Ghomi, M. Tajbakhsh, Z. Kazemi-Kania, Acta Chim. Slov. 2004, 51, 545-550.
Povzetek
V prispevku je prikazana učinkovita priprava substituiranih derivatov dehidrodekalina z Diels-Alderjevo reakcijo med derivati stirencikloheks-2-enona 1 in N-fenilmalenimida. Pri običajni termični reakciji se pri višji temperaturi tvori zmes endo/exo aduktov, medtem ko se v prisotnosti TiCl4 kot katalizatorja tvori izključno endo stereoisomer. Avtorji so selektivnost reakcije potrdili s spektroskopsko in rentgensko strukturno analizo izoliranih endo aduktov.