New Allylphosphonates Derived from (OCH₂CMe₂CH₂O)PCl and Baylis-Hillman Adducts - Stereochemistry and Utility

Abstract

New allylphosphonates have been prepared; an X-ray structural proof for the major Z-isomer has been given for phosphonate 3. Horner-Wadsworth-Emmons reaction of 3 or 6 (Z isomer) with aromatic aldehydes leads to carbomethoxy/ cyano substituted butadienes. In the reaction using cyanoallylphosphonate 6, use of either Z or E isomer leads to the same E,Z product; stereochemistry of one such cyano product is confirmed by X-ray crystallography. In the reaction of 3 with 4-nitrobenzaldehyde stereochemistry for the (E,E) isomer is confirmed by X-ray crystallography.

Key words

allylphosphonates - Baylis-Hillman adducts - 2-substituted butadienes - Horner-Wadsworth-Emmons reaction

References

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7

The Baylis-Hillman adducts ArC(R)(OH)-C(X)=CH₂ were prepared by literature methods. [5a]

8

Typical procedure for 6: To a stirred solution of (Ph)CH(OH)-C(CN)=CH₂ (1.50 g, 9.5 mmol) and Et₃N (0.96 g, 9.5 mmol) in toluene (50 mL), (OCH₂CMe₂CH₂O)PCl(1) (1.6 g, 9.5 mmol) was added dropwise at 0 °C under nitrogen; stirring was continued for 30 min. The precipitate was filtered off, washed with diethyl ether, and the washings added to the filtrate. The combined filtrate was evaporated to dryness and the residue was heated at 110 °C under nitrogen for 3 h by which time rearrange-ment had taken place. The isomers of compound 6 (˜1:1; total yield 80%) so obtained were separated by column chromato-graphy (hexane-ethyl acetate). Isomer a (higher R_f): mp 114-116 °C; IR (cm^-1) 2212, 1604; ¹H NMR δ 1.05, 1.14 (2 s, 6 H, 2 CH ₃), 3.08 [d, ² J(PH) = 22.2 Hz, 2 H, PCH ₂], 3.89-4.30 (m, 4 H, OCH ₂), 7.39-7.54 (m, 6 H, olefinic-H + Ar-H); ¹³C NMR δ 21.4, 21.5, 27.0 [d, ¹ J(PC) = 139.0 Hz], 32.6 [d, ³ J(PC) = 6.2 Hz], 75.7 [d, ² J(PC) = 6.2 Hz], 104.5, 104.8, 119.5, 128.8, 129.1, 130.0, 132.9, 148.1, 148.3; ³¹P NMR δ 17.6. Anal. Calcd for C₁₅H₁₈NO₃P: C, 61.84; H, 6.24; N, 4.81. Found: C, 61.76; H, 6.18; N, 4.74. Isomer b (lower R_f): Mp 128-130 °C; ¹H NMR δ 1.03, 1.07 (2 s, 6 H, 2 CH ₃), 3.01 [d, ² J(PH) = 21.3 Hz, 2 H, PCH ₂], 3.85-4.22 (m, 4 H, OCH ₂), 7.10-7.90 (m, 6 H, olefinic-H + Ar-H); ¹³C NMR δ 21.4, 31.6 [d, ¹ J(PC) = 138.0 Hz], 32.5 [d, ³ J(PC) = 6.2 Hz], 75.6 [d, ² J(PC) = 6.2 Hz], 100.1, 100.3, 118.0, 128.8, 130.6, 133.1, 148.0, 148.2; ³¹P NMR δ 17.8. Anal. Calcd for C₁₅H₁₈NO₃P: C, 61.84; H, 6.24; N, 4.81. Found: C, 61.66; H, 6.16; N, 4.70. The HWE reactions of the phosphonates with the aldehydes were conducted in THF using NaH as the base (supplementary material is available from the authors).

10

Spectral data for compound 9 (mp 70-72 °C): ¹H NMR δ 0.78, 1.28 (2s, 6 H, 2 CH ₃), 3.40 (˜t, ² J ˜ ³ J ˜ 10.2 Hz, 2 H, OCH ₂), 4.24 (d, ³ J ˜ 10.2 Hz, 2 H, OCH ₂), 4.56 [dd, ³ J(PH) ˜ 10.2 Hz, ⁴ J(HH) ˜ 1.0 Hz, 2 H, OCH ₂], 7.21 [s, 1 H, CH=C(CN)], 7.41-7.82 (m, 5 H, Ar-H); ¹³C NMR δ 22.3, 22.7, 32.7 [d, ² J(PC) = 5.0 Hz], 64.2 [d, ² J(PC) = 20.5 Hz], 69.2, 108.6, 117.4, 128.2, 128.9, 129.0, 130.8, 132.8, 144.7; ³¹P NMR δ 121.7. Compound 10 (mp: 168-170 °C). ¹H NMR δ 0.95, 1.05 (2 s, 6 H, 2 CH ₃), 3.75 (˜t, ² J ˜ ³ J ˜ 12.0 Hz, 2 H, OCH ₂), 4.13 [d, ³ J(PH) ˜ 20.0 Hz, 1 H, OCH ₂], 4.15-4.30 (˜m, 2 H, OCH ₂), 6.20 and 6.41 (2 d, ² J ˜ 1.5 Hz, CH ₂=C), 7.25-7.55 (m, 5 H, 5 H, Ar-H); ¹³C NMR δ 21.3, 21.5, 32.6 [d, ³J(PC) = 6.0 Hz], 47.7 [d, ¹ J(PC) = 137.0 Hz, CHPh], 76.2 [d, ² J(PC) = 20.5 Hz], 117.7 (d, J = 10.0 Hz), 118.9, 128.5, 129.0, 129.4, 129.6, 132.9 (J = 6.5 Hz), 134.8 (J = 8.0 Hz); ³¹P NMR 14.6.

11

X-ray data were collected on an Enraf-Nonius-MACH3 at 293 K (3, 12b) or Bruker AXS SMART diffractometer at 296 K(11d) using Mo-K_α (λ = 0.71073 Å) radiation and capillary mounting. The structures were solved by direct methods; [12] all non-hydrogen atoms were refined anisotropically. The quality of data of 11d was only moderate but the stereochemistry is unambiguous. Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 190318 - 190320. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [fax: [phone] or e-mail: [e-mail]]. ORTEP drawings of 11d and 12b are available from the authors.