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.

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

References

Selected references:

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Selected references:

5a Review: Basavaiah D. Rao PD. Hyma RS. Tetrahedron  1996,  52:  8001 

5b Basavaiah D. Pandiaraju S. Tetrahedron  1996,  52:  2261 

5c Aggarwal VK. Mereu A. Tarver GJ. McCague R. J. Org. Chem.  1998,  63:  7183 

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6 Janecki T. Bodalski R. Synthesis  1990,  799 

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).

9 Basavaiah D. Kumaragurubaran N. Padmaja K. Synlett  1999,  1630 

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.

12 Sheldrick GM. SHELX-97   University of Göttingen; Germany: 1997. 

Other reports on the synthesis of 2-substituted-1,3-butadienes:

13a Nakano M. Okamoto Y. Synthesis  1983,  917 

13b Shen Y. Ni J. J. Chem. Res. Synop.  1997,  358 

13c Lee BS. Gil JM. Oh DY. Tetrahedron Lett.  2001,  42:  2345 

14a Janecki T. Synthesis  1991,  167 

14b Janecki T. Bodalski R. Synthesis  1989,  506