Solvent- and Catalyst-Free Conjugate Additions of Organozinc to β-Nitroalkene

Abstract

Conjugate addition of allylzinc and benzylzinc reagents to β-nitroalkenes was carried out without solvent and catalyst at room temperature to give products in high yield.

β-nitroalkenes - allylzinc - benzylzinc - conjugate addition - solvent-free

References and Notes

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<A NAME="RW09107ST-18">18</A>

General Procedure for the Reaction: Organozinc halides RZnX (8 mmol and 10 mmol for allyl bromide and benzyl bromide, respectively) were prepared according to Knochel’s procedure. [17] The solvent (THF) was removed in vacuo and then the nitroalkene (4 mmol) was added slowly. The resulting reaction mixture was stirred for the duration of the given time. After complete conversion, as indicated by TLC, sat. NH₄Cl solution (10 mL) and Et₂O (10 mL) were added and the mixture was stirred for 10 min. The organic layer was separated and washed with sat. brine (10 mL), dried over anhyd MgSO₄ and concentrated. The pure product was obtained by column chromatography of the crude mixture on silica gel using PE-EtOAc as eluent.

<A NAME="RW09107ST-19">19</A>

1-Nitro-2-phenylpent-4-ene (2a): pale yellow oil. IR (KBr): 3073, 3030, 2922, 2853, 1641, 1548, 1451, 1434 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.17-7.34 (m, 5 H), 5.60-5.70 (m, 1 H), 5.02-5.09 (m, 2 H), 4.51-4.64 (m, 2 H), 3.52-3.60 (m, 1 H), 2.38-2.56 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 134.1, 128.8, 127.6, 127.4, 118.1, 79.8, 43.7, 37.6. EI-MS: m/z = 241 [M⁺], 211, 104, 91, 77. Anal. Calcd for C₁₁H₁₃NO₂: C, 69.09; H, 6.85; N, 7.32. Found: C, 68.46; H, 6.93; N, 6.57.

<A NAME="RW09107ST-20">20</A>

1-Nitro-3-phenyl-2-(2-furyl)propane (3l): yellow oil. IR (KBr): 3063, 3030, 2924, 2860, 1551, 1501, 1451, 1431cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.37 (dd, J = 0.8, 2.0 Hz, 1 H), 7.20-7.30 (m, 3 H), 7.06-7.08 (m, 2 H), 6.26-6.27 (m, 1 H), 6.03-6.04 (m, 1 H), 4.61 (dd, J = 8.0, 12.8 Hz, 1 H), 4.52 (dd, J = 6.4, 12.8 Hz, 1 H), 3.85-3.92 (m, 1 H), 3.11 (dd, J = 7.6, 13.6 Hz, 1 H), 2.94 (dd, J = 7.6, 13.6 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.9, 142.2, 137.4, 129.0, 128.6, 127.0, 110.4, 107.5, 77.3, 39.6, 37.3. EI-MS: m/z = 231 [M⁺], 184, 91, 77. Anal. Calcd for C₁₃H₁₃NO₃: C, 67.52; H, 5.67; N, 6.06. Found: C, 68.16; H, 5.27; N, 5.40.