An Efficient DABCO-Catalyzed Ireland-Claisen Rearrangement of Allylic Acrylates

Abstract

A novel DABCO-catalyzed Ireland-Claisen [3,3]-rearrangement of allylic acrylates to give α-methylene-γ,δ-unsaturated carboxylic acids in the presence of an excess of TMSCl and DBU in refluxing acetonitrile was developed. The protocol provides an easy entry to α-methylene-γ,δ-unsaturated carboxylic acids from ­allylic alcohols in good yields.

DABCO - allylic acrylates - Ireland-Claisen rearrangement - α-methylene-γ,δ-unsaturated carboxylic acids

References and Notes

1 For an excellent review on the thermal, aliphatic Claisen rearrangement, see: Ziegler FE. Chem. Rev.  1988,  88:  1423 

2a Ireland RE. Mueller RH. J. Am. Chem. Soc.  1972,  94:  5897 

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13 The unexpected superiority of DABCO over more basic tertiary amine catalysts in the Baylis-Hillman reaction between acrylamide and aldehydes has been reported. See: Faltin C. Fleming EM. Connon SJ. J. Org. Chem.  2004,  69:  6496 

14 Shieh W. Dell S. Bach A. Repič O. Blacklock TJ. J. Org. Chem.  2003,  68:  1854 

15

General Procedure of the Rearrangement.
A reaction flask was charged with the allylic acrylate 3 (32.4 mmol), DABCO (0.73 g, 6.5 mmol), TMSCl (10.58 g, 97.4 mmol), DBU (9.90 g, 65.0 mmol) and MeCN (75 mL). The mixture was heated under reflux and the reaction was monitored by GC or TLC until the reaction was complete (reaction time as specified in Table [1] ). Then, the volatiles were removed under reduced pressure. The residue was suspended in Et₂O (100 mL) and stirred with 3 N HCl (40 mL) for a couple of minutes. The organic layer was separated, and washed sequentially with brine and H₂O, dried over anhyd MgSO₄ and concentrated in vacuo. The residue was purified by column chromatography or subjected to bulb-to-bulb distillation or recrystallization from EtOH to afford the pure compounds 4a-h as a colorless oil and 4i-j as a white solid (Table [1] ).

16 Ghosh N. Synlett  2004,  574 

17

All new compounds have been isolated in pure form and characterized by spectral data (NMR, IR and MS).
Selected Data for Compounds 4.
Compound 4c: ¹H NMR (300 MHz, CDCl₃): δ = 12.23 (br, 1 H), 6.33 (s, 1 H), 5.67 (br s, 1 H), 5.52 (dd, J = 15.5, 6.1 Hz, 1 H), 5.42 (dt, J = 15.5, 6.1 Hz, 1 H), 2.99 (d, J = 6.1 Hz, 2 H), 2.30 (dsept, J = 6.1, 6.8 Hz, 1 H), 1.00 (2 d, J = 6.8 Hz, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 173.0 (s), 140.5 (d), 139.5 (s), 127.3 (t), 123.0 (d), 34.1 (t), 31.1 (d), 22.4 (2q). IR (KBr): ca. 3000, 1698, 1436, 1289, 1158, 952 cm^-1. MS (EI): m/z = 154 [M]⁺, 111 [M - C₃H₇]⁺.
Compound 4e: ¹H NMR (300 MHz, CDCl₃): δ = ca. 11.1 (br, 1 H), 6.32 (s, 1 H), 5.68 (s, 1 H), 5.15 (t, J = 7.2 Hz, 1 H), 3.03 (d, J = 7.2 Hz, 2 H), 2.08 (br q, J = 7.5 Hz, 2 H), 2.07 (q, J = 7.5 Hz, 2 H), 1.03 (t, J = 7.5 Hz, 3 H), 0.97 (t, J = 7.5 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 173.1 (s), 145.6 (s), 139.5 (s), 126.9 (t), 118.2 (d), 29.2 (2 t), 23.2 (t), 12.1 (q), 12.8 (q). IR (KBr): ca. 3000, 1698, 1629, 1434, 1283, 1155, 954 cm^-1. MS (EI): m/z = 168 [M]⁺, 139 [M - C₂H₅]⁺.
Compound 4f (major trans-isomer): ¹H NMR (300 MHz, CDCl₃): δ = ca. 11.0 (br, 1 H), 6.31 (s, 1 H), 5.65 (s, 1 H), 5.23 (t, J = 7.2 Hz, 1 H), 3.01 (d, J = 7.2 Hz, 2 H), 2.30 (sept, J = 6.8 Hz, 1 H), 1.60 (s, 3 H), 1.03 (2 d, J = 6.8 Hz, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 173.1 (s), 144.1 (s), 139.1 (s), 126.8 (t), 117.6 (d), 36.8 (d), 29.4 (t), 21.4 (2q), 13.3 (q). IR (KBr,): ca. 3000, 1695, 1630, 1434, 1284, 1156, 952
cm^-1. MS (EI): m/z = 168 [M]⁺, 125 [M - C₃H₇]⁺.
Compound 4j: ¹H NMR (300 MHz, CDCl₃): δ = 7.34 (d, J = 11.4 Hz, 1 H), 6.55 (dd, J = 14.7, 10.5 Hz, 1 H), 6.39 (dd, J = 14.7, 11.4 Hz, 1 H), 6.22 (dd, J = 14.1, 10.5 Hz, 1 H), 5.96 (dq, J = 14.1, 6.8 Hz, 1 H), 1.95 (s, 3 H), 1.85 (d, J = 6.8 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 173.7 (s), 141.0 (2 d), 135.0 (d), 131.6 (d), 125.2 (d), 125.0 (s), 18.6 (q), 12.3 (q). IR: (KBr): ca. 3000, 1678, 1601, 1427, 1316, 1268, 987, 929 cm^-1. MS (EI): m/z = 152 [M]⁺, 107 [M - CO₂H]⁺.
Compound 4k: ¹H NMR (400 MHz, CDCl₃): δ = 6.47 (s, 1 H), 5.92 (s, 1 H), 5.75 (s, 1 H), 3.19 (s, 2 H), 2.24 (s, 2 H), 2.22 (s, 2 H), 1.05 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 28.3 (2 q), 33.7 (s), 39.6 (t), 43.8 (t), 51.0 (t), 125.8 (d), 130.3 (t), 136.0 (s), 161.1 (s), 171.1 (s), 200.6 (s). IR: (KBr): ca. 3000, 2929, 1720, 1667, 1372, 1160, 982 cm^-1. MS (EI): m/z = 208 [M]⁺, 163 [M - CO₂H]⁺.

18 For a computational study on boat or chair preferences in the Ireland-Claisen rearrangements of cylohexenyl silyl ketene acetals, see: Khaledy MM. Kalani MYS. Khuong KS. Houk KN. J. Org. Chem.  2003,  68:  572 

19 For a review on this topic, see: Hoffmann HMR. Rabe J. Angew. Chem., Int. Ed. Engl.  1985,  24:  94 

20 Cateni F. Zilic J. Zacchigna M. Bonivento P. Frausin F. Scarcia V. Eur. J. Med. Chem.  2006,  41:  192 ; and references cited therein