A General, Polymer-Supported Acid Catalyzed Hetero-Michael Addition

Abstract

Hetero-Michael additions of nitrogen, oxygen and sulfur nucleophiles to α,β-unsaturated ketones were efficiently catalyzed by Nafion^® SAC-13 perfluorinated resinsulfonic acid.

Key words

hetero-Michael additions - heterogeneous catalysis - enones - polymer-support - Nafion^®

References

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• 16 Analytical data for 5-(benzyloxycarbonylamino)hexan-3-one: ¹H NMR (400 MHz, CDCl₃): δ = 1.00 (t, J = 7.3 Hz, 3 H), 1.19 (d, J = 6.7 Hz, 3 H), 2.38 (q, J = 7.3 Hz, 2 H), 2.53 (dd, J = 5.9 Hz, 15.7 Hz, 1 H), 1.65 (dd, J = 4.8 Hz, 15.7 Hz, 1 H), 4.00-4.10 (m, 1 H), 5.05 (s, 2 H), 5.33 (br, 1 H), 7.22-7.38 (m, 5 H). ¹³C NMR (100 MHz, CDCl₃): δ = 7.9, 20.9 (CH₃), 36.9 (CH₂), 44.3 (CH), 48.2, 66.9 (CH₂), 128.4, 128.7, 129.9 (Ar-C), 137.0 (ipso-Ar-C), 156.0, 210.5 (C=O). IR (neat, film): cm^-1 3323, 3061, 2975, 1706, 1680, 1534, 1254. HRMS [+ESI]: calc. 272.1263, found: 272.1250 ([C₁₄H₁₉NO₃Na]⁺). Mp: 55-57 °C
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10

Experimental procedure: Enone (0.25 mmol) and nucleophile (0.375 mmol, 1.5 equiv.) were dissolved in CH₃CN (0.5 mL) and stirred over Nafion^® SAC-13 (15 mg, 60 g˙mol^-1) at room temperature. The reaction was monitored by TLC and the product was isolated by preparative TLC after filtering off the catalyst.

12

The ion exchange capacity of Nafion^® SAC-13 is 0.12 mmolg^-1 according to ref. [9b]

14

Only sluggish conversion was observed with acetacrylimide and benzyl carbamate: 34% yield (48 h) with Pd(CH₃CN)₄(BF₄)₂; 84% yield (72 h) with Tf₂NH (see ref. [7] ).

15

Catalyst regeneration: Spent Nafion^® SAC-13 was stirred over 6 N HCl (0.5 mL) overnight. After filtration, the catalyst was dried in vacuo for 20 h and reused.