Diels‐Alder Reaction of Cyclopentadiene with Acrylic Acid Derivatives in Heterogeneous Phases

Abstract

In the addition of the acrylic acid derivatives (la)-(lc) to cyclopentadiene in homogeneous phases, the isomeric ratio of the products is hardly influenced by solvents or catalysts"]; for the dienophiles acrolein (la) and methyl acrylate (lb), the ratio of endo-to exo-adducts is ca. 3 : 1, and, in contrast, ca. 3 : 2 for acrylonitrile (lc).Table I. Percentage composition of the product mixtures of the Diels-Alder reaction of cyclopentadiene with acrylic acid derivatives absorbed on various activated surfaces. The values in brackets refer to reactions on non-activated surfaces [a]. ( I ) Silica gel (2) (3) (a) 22.0 77.7 (19.2) (80. I) (b) 10.5 87.5 (13.2) (84.3) (c) 32.8 50.4 (35.8) (60.1) Montigel PI (2) (3) 27.7 68.9 (20.4) (79.6) 6.6 90.7 (12.9) (83.4) 25.9 67.2 (32.0) (65.0) A1203 (neutral) (2) (3) 43.9 47.3 (48.8) (51.2) 2.9 93.7 (2.8) (93.8) 37.0 60.3 (38.3) (58.1) Sea sand (2) (3) 31.3 68.0 (22.6) (76.5) 23.5 71.1 (24.2) (72.2) 37.5 59.0 (38.0) (57.5) Cellulose (2) 13) 25.1 73.9 (26.7) (72.8) 24.3 71.4 (23.6) (72.5) 36.5 57.0 (36.7) (58.4) [a] In homogeneous phases (2 h at 60"C), cyclopentadiene and (la), (lb). or (Ic) give the following product ratios: (2a) :(3a)=24.4 :75.3; (26):(36)=24.2:71.5; (2c):(3~)=40.2:58.2. [b] Montigel is a natural montmorrillonite.We have managed to achieve an isomer ratio of almost I : 1 in a purely heterogeneous reaction of cyclopentadiene with acrolein (la) on non-activated neutral A1203. In the addition of acrylonitrile (lc) to cyclopentadiene on activated Montigel, considerably more endo-isomer (3c) is formed than in the same reaction under homogeneous conditions. Even more impressive is that the formation of the exo-isomer is almost completely blocked in the reaction of methyl acrylate (lb) with cyclopentadiene on non-activated Al2O3 ( Table 1). The isomer ratios are almost independent of temperature (40-70°C). Mutual condensation of the adducts can be excluded, since these are stable under the same reaction conditions.Measurements of the absorption behavior of the starting materials at a maximal covering density of loT5 particles/ cmz on a variety of surfaces, over different pressure and temperature ranges, indicate that the chemical composition of the absorbent only influences the covering density to a small extent (the bond strength is 25 kcal/mol); any special interaction of the educt with the surface, which could result in reduction in the intramolecular interactions, is therefore precluded"'. Presumably, a small fraction of the molecules is strongly adsorbed on the surface. Under these conditions one of the two transition states is stabilized over the other by symmetry-controlled secondary orbital interactions[31. ProcedureSolutions of cyclopentadiene (0.05 mol), prepared by thermolysis of dicyclopentadiene, and of the freshly distilled acrylic acid derivatives (0.05 mol), each in 50 mL of diethyl ether, are taken up successively on 30 mg of one of the carrier substances at 20°C. After cautious evaporation of the solvent at 35 "C at atmospheric pressure, the heterog...

Silica-Promoted Diels−Alder Reactions in Carbon Dioxide from Gaseous to Supercritical Conditions

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Multi-step organic synthesis using solid-supported reagents and scavengers: a new paradigm in chemical library generation

“…A range of inorganic supports have also been used for this transformation. 1344,1345,1346 1347 1347 Silica supported catalysts have also been used for this transformation: 1348 Proline based supports have also been used (up to 54% ee). 1349 1350 endo:exo ratio varied with the solvent used.…”

Synthesis and application of L-serine derivative ligands in Diels-Alder reaction between cyclopentadiene and methyl acrylate

“…No further purifications were needed. 5): 1 H NMR (400 MHz, CDCl 3 ): δ = 7.79 (d, J = 7.5 Hz, 2H, H ar-Fluoren ), 7.62 (d, J = 7.4 Hz, 2H, H ar-Fluoren ), 7.39-7.45 (m, 2H ar ), 7.28-7.38 (m, 7H ar ), 6.91 (bs, 1H, NH), 5.79 (bs, 1H, NH), 4.47-4.57 (sl, 2H, CH 2 Ph), 4.44 (d, J = 6.8 Hz, 2H, COOCH 2 ), 4.28 (sl, 1H, COCH), 4.24 (t, J = 7.0 Hz, 1H, CH Fluoren ), 3.87 (dd, J = 8.6, 3.7 Hz, 1H, OCH a CH b ), 3.42 (t, J = 8.0 Hz, 1H, OCH a CH b ), 1.17 (s, 9 H, C(CH 3 ) 3 ); 13 Serines (10,11): Piperidine (2 eq.) was added to a solution of serines 6/7 in anhydrous DMF (5 ml).…”

“…The acid catalyzed Diels-Alder reactions, namely between cyclopentadiene (CPD) and acrylates, is well documented, [1,[3][4][5][6][7][8][9][10][11][12][13][14][15] the most important used Lewis acids being Al(III), Fe(III) or boron complexes. The use of such strong acids is needed because ester dienophiles (as acrylate ones) are not very reactive.…”