A Facile Method for the Stereoselective Preparation of (1Z,3E)-Dienyl Ethers via 1,4-Elimination of 1,4-Dialkoxy-(2Z)-alkenes with n-Butyllithium

Abstract

Treatment of 1-alkoxy-4-methoxy-(2Z)-alkenes or 1-sil­oxy-4-methoxy-(2Z)-alkenes with n-butyllithium in diethyl ether is shown to afford the corresponding (1Z,3E)-dienyl, alkyl or silyl ethers, respectively, in high stereoselectivity via a facile 1,4-elimination. The scope and the regio- and stereochemical features of the synthetic method are described.

Key words

1,4-eliminations - dienyl ethers - dienyl acetals - stereoselective synthesis - precoordinations

References and Notes

• For reviews, see:
• 1a Tomooka K. In The Chemistry of Organolithium Compounds   Vol. 2:  Rappoport Z. Marek I. John Wiley and Sons Ltd.; Chichester: 2004.  p.749-828  
• 1b Clayden J. In Organolithiums: Selectivity for Synthesis   Baldwin JE. Williams RM. Pergamon; Manchester: 2002.  Chap. 8.
• 1c Tomooka K. Yamamoto H. Nakai T. Liebigs Ann./Recl.  1997,  1275 
• 1d Nakai T. Mikami K. Org. React.  1994,  46:  105 
• 1e Brückner R. In Comprehensive Organic Synthesis   Vol. 6:  Trost BM. Fleming I. Pergamon; Oxford: 1991.  Chap. 4.6.
• 2a Casiraghi G. Zanardi F. Appendino G. Rassu G. Chem. Rev.  2000,  100:  1929 
• 2b Ishida A. Mukaiyama T. Bull. Chem. Soc. Jpn.  1977,  50:  1161 
• 3a Inui M. Hosokawa S. Nakazaki A. Kobayashi S. Tetrahedron Lett.  2005,  46:  3245 
• 3b Suzuki T. Inui M. Hosokawa S. Kobayashi S. Tetrahedron Lett.  2003,  44:  3713 
• 4 Danishefsky S. Kitahara T. J. Am. Chem. Soc.  1974,  96:  7807 
• 5 For a review of 1,3-dienyl silyl ethers (silyl dienol ethers), see: Brownbridge P. Synthesis  1983,  85 
• Previous preparation of 1,3-dienyl silyl ethers:
• 6a Choi J. Imai E. Mihara M. Oderaotoshi Y. Minakata S. Komatsu M. J. Org. Chem.  2003,  68:  6164 
• 6b Janey JM. Iwama T. Kozmin SA. Rawal VH. J. Org. Chem.  2000,  65:  9059 
• 6c Moreno MJSM. Martins RMLM. Melo MLS. Neves ASC. Chem. Lett.  1997,  529 
• 6d Tominaga Y. Kamio C. Hosomi A. Chem. Lett.  1989,  1761 
• 6e Iqbal J. Khan MA. Synth. Commun.  1989,  19:  515 
• 6f Cazeau P. Duboudin F. Moulines F. Babot O. Dunogues J. Tetrahedron  1987,  43:  2089 
• 6g Colvin EW. Thom IG. Tetrahedron  1986,  42:  3137 
• 6h Casey CP. Jones CR. Tukada H. J. Org. Chem.  1981,  46:  2089 
• 6i Hirai K. Suzuki H. Morooka Y. Ikawa T. Tetrahedron Lett.  1980,  21:  3413 
• 6j Miller RD. McKean DR. Synthesis  1979,  730 
• 6k House HO. Czuba LJ. Gall M. Olmstead HD. J. Org. Chem.  1969,  34:  2324 
• Previous preparation of alkyl 1,3-dienyl ethers:
• 7a Gilbert JC. Weerasooriya U. J. Org. Chem.  1983,  48:  448 
• 7b Hiranuma H. Miller SI. J. Org. Chem.  1982,  47:  5083 
• 7c Dowd P. Weber W. J. Org. Chem.  1982,  47:  4774 
• 7d Kluge AF. Cloudsdale IS. J. Org. Chem.  1979,  44:  4847 
• 7e Earnshaw C. Wallis CJ. Warren S. J. Chem. Soc., Perkin Trans. 1  1979,  3099 
• 8 A similar type of 1,4-elimination reaction has been reported using alkenyl acetals: Canepa C. Prandi C. Sacchi L. Venturello P. J. Chem. Soc., Perkin Trans. 1  1993,  1875 
• 16 Hartung J. Kneuer R. Eur. J. Org. Chem.  2000,  1677 

9

Prepared in three steps: (i) t-BuMe₂SiOCH₂CºCH, n-BuLi, THF, -78 °C then n-BuCHO, -78 °C to r.t.; (ii) NaH, MeI, THF, 0 °C to r.t.; (iii) H₂ (1 atm), 5% Lindlar cat., quinoline, MeOH, r.t.

10

All stereoisomers were identified by ¹H NMR comparisons of the authentic samples prepared from (EtO)₂P(O)CH₂OP via the literature procedure (ref. 7d).

11

Prepared from POCH₂CºCH according to the same three-step procedure as described for 1b (ref. 9).

12

Typical Procedure for the Preparation of 1,3-Dienyl Ethers 2 To a solution of 1 (1.0 equiv, 0.25 M) in Et₂O was added a 1.6 M n-BuLi solution in n-hexane (1.5 equiv) at -40 °C to 0 °C and the mixture was stirred for 2-4 h at the same temperature. The resulting mixture was quenched with H₂O and extracted with Et₂O. The combined extract was washed with brine, dried over NaSO₄ and concentrated. The residue was purified by chromatography on silica gel to afford the corresponding 1,3-dienyl ether 2.
Selected Spectroscopic Data(2 Z )-1-( tert -Butyldimethylsilyloxy)-4-methoxy-2-butene ( 1a) Colorless oil. ¹H NMR (270 MHz, CDCl₃): δ = 5.70 (1 H, dtt, J = 11.1, 5.9, 1.4 Hz, 2- or 3-H), 5.57 (1 H, dtt, J = 11.1, 5.9, 1.4 Hz, 2- or 3-H), 4.24 (1 H, dd, J = 5.9, 1.4 Hz, 1-H), 3.99 (1 H, dd, J = 5.9, 1.4 Hz, 4-H), 3.33 (3 H, s, OCH₃), 0.90 [9 H, s, SiC(CH₃)₃], 0.07 [6 H, s, Si(CH₃)₂]. ¹³C NMR (68 MHz, CDCl₃): δ = 132.6, 126.7, 68.3, 59.5, 58.0, 26.0, 18.4, -5.0. IR (film): 3020, 2948, 2924, 2884, 2852, 1475, 1470, 1406, 1362, 1334, 1254, 1190, 1092, 1006, 956, 912, 838, 776 cm^-1. Anal. Calcd for C₁₁H₂₄O₂Si: C, 61.05; H, 11.18. Found: C, 61.17; H, 11.48.
(2 Z )-1-(Benzyloxymethoxy)-4-methoxy-2-octene ( 1f) Colorless oil. ¹H NMR (270 MHz, CDCl₃): δ = 7.40-7.27 (5 H, m, Ph), 5.82-5.72 (1 H, m, 2-H), 5.49-5.39 (1 H, m, 3-H), 4.78 (2 H, s, OCH₂O), 4.62 (2 H, s, OCH₂Ph), 4.27 (1 H, ddd, J = 12.4, 7.3, 1.4 Hz, 1-CH₂), 4.15 (1 H, ddd, J = 12.4, 6.1, 1.4 Hz, 1-CH₂), 3.94-3.85 (1 H, m, 4-H), 3.25 (3 H, s, OCH₃), 1.68-1.52 (1 H, m, 5-CH₂), 1.47-1.18 (5 H, m, 5-, 6-, and 7-CH₂), 0.88 (3 H, t, J = 6.8 Hz, 8-CH₃). ¹³C NMR (68 MHz, CDCl₃): δ = 137.6, 134.2, 128.7, 128.3, 127.7, 127.6, 93.8, 76.6, 69.3, 63.2, 56.1, 35.2, 27.4, 22.7, 14.1. IR (film): 3060, 3024, 2928, 2872, 2816, 1496, 1454, 1402, 1380, 1206, 1190, 1168, 1102, 1048, 962, 958, 736, 698 cm^-1. Anal. Calcd for C₁₇H₂₆O₃: C, 73.34; H, 9.41. Found: C, 73.42; H, 9.63.
(1 Z )-1-( tert -Butyldimethylsilyloxy)-1,3-butadiene ( 2a) [16]
Colorless oil; purified by chromatography on silica gel (hexane-Et₂O = 100:1 to 20:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.76 (1 H, dddd, J = 17.3, 10.7, 10.3, 1.1 Hz, 3-H), 6.19 (1 H, ddd, J = 5.9, 1.1, 1.1 Hz, 1-H), 5.20 (1 H, dd, J = 10.7, 5.9 Hz, 2-H), 5.07 (1 H, m, J = 17.3, 2.0 Hz, 4 _cis -H), 4.89 (1 H, ddd, J = 10.3, 2.0, 1.1 Hz, 4 _trans -H), 0.94 [9 H, s, SiC(CH₃)₃], 0.16 [6 H, s, Si(CH₃)₂]. ¹³C NMR (68 MHz, CDCl₃): δ = 140.4, 129.8, 112.9, 111.1, 25.7, 18.4, -5.3. IR (film): 3080, 2952, 2928, 2884, 2856, 1642, 1594, 1472, 1438, 1392, 1362, 1254, 1174, 1080, 998, 928, 890, 840, 784 cm^-1.
(1 Z ,3 E )-1-( tert -Butyldimethylsilyloxy)-1,3-octadiene ( 2b) Colorless oil; purified by chromatography on silica gel (hexane-EtOAc = 100:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.40 (1 H, ddd, J = 15.6, 10.8, 1.1 Hz, 3-H), 6.09 (1 H, d, J = 5.9 Hz, 1-H), 5.55 (1 H, dt, J = 15.6, 6.8 Hz, 4-H), 5.13 (1 H, dd, J = 10.8, 5.9 Hz, 2-H), 2.14-2.02 (2 H, dt, J = 6.8, 6.8 Hz, 5-CH₂), 1.44-1.24 (4 H, m, 6-CH₂ and 7-CH₂), 0.94 [9 H, s, SiC(CH₃)₃], 0.89 (3 H, t, J = 7.0 Hz, 8-CH₃), 0.15 [6 H, s, Si(CH₃)₂]. ¹³C NMR (68 MHz, CDCl₃): δ = 138.2, 130.9, 122.8, 110.8, 32.7, 31.8, 25.7, 22.4, 18.4, 14.1, -5.2. IR (film): 3028, 2952, 2924, 2852, 1654, 1612, 1470, 1410, 1362, 1254, 1156, 1112, 1050, 1006, 972, 838, 780 cm^-1. Anal. Calcd for C₁₄H₂₈OSi: C, 69.93; H, 11.74. Found: C, 69.70; H, 12.03.
(1 Z ,3 E )-1-( tert -Butyldimethylsilyloxy)-4-methoxy-1,3-butadiene ( 2c) Pale yellow oil; purified by chromatography on silica gel (hexane-Et₂O = 30:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.55 (1 H, d, J = 13.0 Hz, 4-H), 6.06 (1 H, d, J = 5.9 Hz, 1-H), 5.84 (1 H, dd, J = 13.0, 10.8 Hz, 3-H), 5.05 (1 H, dd, J = 10.8, 5.9 Hz, 2-H), 3.59 (3 H, s, OCH₃), 0.94 [9 H, s, SiC(CH₃)₃], 0.15 [6 H, s, Si(CH₃)₂]. ¹³C NMR (68 MHz, CDCl₃): δ = 148.2, 136.6, 106.5, 98.9, 56.2, 25.7, 18.4, -5.2. IR (film): 2948, 2928, 2892, 2852, 1656, 1608, 1470, 1406, 1362, 1332, 1256, 1208, 1166, 1136, 1124, 1064, 938, 838, 780 cm^-1. Anal. Calcd for C₁₁H₂₂O₂Si: C, 61.63; H, 10.34. Found: C, 61.58; H, 10.61.
(1 Z ,3 E )-1-(1-Ethoxyethoxy)-1,3-octadiene ( 2d) Pale yellow oil; purified by chromatography on silica gel (hexane-EtOAc = 70:1 to 40:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.39 (1 H, ddd, J = 15.4, 10.8, 1.4 Hz, 3-H), 6.12 (1 H, d, J = 5.9 Hz, 1-H), 5.57 (1 H, dt, J = 15.4, 7.0 Hz, 4-H), 5.12 (1 H, dd, J = 10.8, 5.9 Hz, 2-H), 4.94 (1 H, q, J = 5.4 Hz, OCHO), 3.74 (1 H, dq, J = 9.5, 7.2 Hz, OCH₂CH₃), 3.49 (1 H, dq, J = 9.5, 7.2 Hz, OCH₂CH₃), 2.12-2.04 (2 H, dt, J = 7.0, 6.8 Hz, 5-CH₂), 1.43-1.25 (4 H, m, 6-CH₂ and 7-CH₂), 1.39 [3 H, d, J = 5.4 Hz, OCH(CH₃)O], 1.21 (3 H, t, J = 7.2 Hz, OCH₂CH₃), 0.89 (3 H, t, J = 7.0 Hz, 8-CH₃). ¹³C NMR (68 MHz, CDCl₃): δ = 138.9, 131.5, 122.8, 108.1, 100.9, 62.5, 32.7, 31.8, 22.4, 20.6, 15.2, 14.0. IR (film): 3036, 2956, 2924, 2872, 1656, 1618, 1444, 1382, 1342, 1276, 1226, 1150, 1134, 1112, 1080, 1052, 974, 880, 830, 748 cm^-1. Anal. Calcd for C₁₂H₂₂O₂: C, 72.68; H, 11.18. Found: C, 72.52; H, 11.47.
(1 Z ,3 E )-1-(Methoxymethoxy)-1,3-octadiene ( 2e) Colorless oil; purified by chromatography on silica gel (hexane-EtOAc = 70:1 to 40:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.39 (1 H, ddd, J = 15.5, 10.9, 1.1 Hz, 3-H), 6.03 (1 H, d, J = 6.2 Hz, 1-H), 5.60 (1 H, dt, J = 15.5, 7.0 Hz, 4-H), 5.17 (1 H, dd, J = 10.9, 6.2 Hz, 2-H), 4.83 (2 H, s, OCH₂O), 3.42 (3 H, s, OCH₃), 2.16-2.02 (2 H, dt, J = 7.0, 6.8 Hz, 5-CH₂), 1.45-1.23 (4 H, m, 6-CH₂ and 7-CH₂), 0.90 (3 H, t, J = 7.0 Hz, 8-CH₃). ¹³C NMR (68 MHz, CDCl₃): δ = 141.2, 132.2, 122.4, 108.9, 96.4, 55.8, 32.7, 31.7, 22.4, 14.1. IR (film): 3036, 2952, 2920, 1658, 1618, 1464, 1386, 1306, 1242, 1160, 1114, 1042, 974, 924, 830, 750 cm^-1. Anal. Calcd for C₁₀H₁₈O₂: C, 70.55; H, 10.66. Found: C, 70.38; H, 10.75.
(1 Z ,3 E )-1-(Benzyloxymethoxy)-1,3-octadiene ( 2f) Colorless oil; purified by chromatography on silica gel (hexane-EtOAc = 80:1 to 50:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 7.37-7.27 (5 H, m, Ph), 6.40 (1 H, ddd, J = 15.4, 10.8, 1.1 Hz, 3-H), 6.10 (1 H, d, J = 6.2 Hz, 1-H), 5.61 (1 H, dt, J = 15.4, 7.0 Hz, 4-H), 5.19 (1 H, dd, J = 10.8, 6.2 Hz, 2-H), 4.95 (2 H, s, OCH₂O), 4.65 (2 H, s, OCH₂Ph), 2.16-2.06 (2 H, dt, J = 7.0, 6.8 Hz, 5-CH₂), 1.45-1.25 (4 H, m, 6-CH₂ and 7-CH₂), 0.90 (3 H, t, J = 7.0 Hz, 8-CH₃). ¹³C NMR (68 MHz, CDCl₃): δ = 141.2, 137.0, 132.2, 128.3, 128.0, 127.8, 122.4, 109.0, 94.3, 69.8, 32.7, 31.7, 22.4, 14.1. IR (film): 3032, 2952, 2924, 2868, 1658, 1618, 1496, 1454, 1380, 1300, 1226, 1172, 1116, 1042, 974, 904, 832, 744, 696 cm^-1. Anal. Calcd for C₁₆H₂₂O₂: C, 78.01; H, 9.00. Found: C, 78.16; H, 9.21.
(1 Z ,3 E )-1-(1-Methoxy-1-methylethoxy)-1,3-octadiene ( 2g) Pale yellow oil; purified by chromatography on silica gel (hexane-EtOAc = 80:1 to 60:1 as eluent). ¹H NMR (270 MHz, C₆D₆): δ = 6.83 (1 H, ddd, J = 15.5, 10.7, 1.1 Hz, 3-H), 6.32 (1 H, d, J = 6.2 Hz, 1-H), 5.61 (1 H, dt, J = 15.5, 7.0 Hz, 4-H), 5.30 (1 H, dd, J = 10.7, 6.2 Hz, 2-H), 3.01 (3 H, s, OCH₃), 2.13-2.01 (2 H, dt, J = 7.0, 6.5 Hz, 5-CH₂), 1.38-1.15 [10 H, m, OC(CH₃)₂O and 6, 7-CH₂], 0.81 (3 H, t, J = 7.0 Hz, 8-CH₃). ¹³C NMR (68 MHz, C₆D₆): δ = 137.0, 131.0, 124.2, 108.9, 101.9, 48.9, 33.2, 32.3, 25.0, 22.8, 14.3. IR (film): 3032, 2988, 2952, 2924, 2852, 1656, 1616, 1464, 1402, 1374, 1264, 1218, 1184, 1138, 1106, 1072, 1032, 974, 868, 782, 750 cm^-1. Anal. Calcd for C₁₂H₂₂O₂: C, 72.68; H, 11.18. Found: C, 72.55; H, 11.44.
(1 Z ,3 E )-1-(2-Tetrahydropyranyloxy)-1,3-octadiene ( 2h) Pale yellow oil; purified by chromatography on silica gel (hexane-EtOAc = 70:1 to 40:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.42 (1 H, ddd, J = 15.5, 10.9, 0.8 Hz, 3-H), 6.10 (1 H, d, J = 5.9 Hz, 1-H), 5.59 (1 H, dt, J = 15.5, 7.3 Hz, 4-H), 5.16 (1 H, dd, J = 10.9, 5.9 Hz, 2-H), 4.94 (1 H, t, J = 3.1 Hz, OCHO), 3.85 (1 H, ddd, J = 11.2, 9.5, 3.5 Hz, THP-6-CH₂), 3.62-3.52 (1 H, m, THP-6-CH₂), 2.16-2.04 (2 H, dt, J = 7.3, 6.8 Hz, 5-CH₂), 1.99-1.11 (10 H, m, THP-3,4,5-CH₂ and 6,7-CH₂), 0.90 (3 H, t, J = 7.3 Hz, 8-CH₃). ¹³C NMR (68 MHz, CDCl₃): δ = 140.8, 131.8, 122.6, 108.4, 98.5, 61.9, 32.7, 31.8, 29.7, 25.2, 22.4, 18.7, 14.1. IR (film): 3032, 2946, 2924, 2868, 1658, 1618, 1454, 1356, 1242, 1202, 1124, 1028, 970, 904, 872, 816, 750 cm^-1. Anal. Calcd for C₁₃H₂₂O₂: C, 74.24; H, 10.54. Found: C, 74.25; H, 10.78.
(1 Z ,3 E )-1-( tert -Butyldimethylsilyloxy)-6-methyl-1,3,5-heptatriene ( 2i) Colorless oil; purified by chromatography on silica gel (hexane-Et₂O = 50:1 to 20:1 as eluent). ¹H NMR (270 MHz, CDCl₃): δ = 6.48 (1 H, dd, J = 15.1, 10.5 Hz, 3-H), 6.30 (1 H, dd, J = 15.1, 10.8 Hz, 4-H), 6.17 (1 H, d, J = 5.7 Hz, 1-H), 5.93-5.86 (1 H, m, 5-H), 5.24 (1 H, dd, J = 10.5, 5.7 Hz, 2-H), 1.79 [3 H, s, C(CH₃)₂], 1.76 [3 H, s, C(CH₃)₂], 0.94 [9 H, s, SiC(CH₃)₃], 0.16 [6 H, s, Si(CH₃)₂]. ¹³C NMR (68 MHz, CDCl₃): δ = 139.5, 134.0, 125.9, 125.6, 123.2, 111.3, 26.2, 25.7, 18.4, -5.2. IR (film): 3028, 2952, 2924, 2856, 1646, 1628, 1584, 1470, 1408, 1274, 1256, 1236, 1140, 1066, 1032, 1006, 986, 964, 838, 780 cm^-1. Anal. Calcd for C₁₄H₂₆OSi: C, 70.52; H, 10.99. Found: C, 70.78; H, 11.23.

13

Use of s-BuLi or t-BuLi in Et₂O instead of n-BuLi gave the same results, which suggests that the aggregation states of n-BuLi under our reaction conditions are monomer or dimer, since t-BuLi becomes dimeric in Et₂O without substrates.

14

The complete 1Z-to-1E changeover was observed in the case of 1d. The reaction of silyl derivative 1b in THF under the same conditions gave a mixture of stereoisomers without any detectable retro-Brook rearrangement product:
(1Z,3E)/(1Z,3Z)/(1E,3E)/(1E,3Z) = 42:1:16:21 (yield, %).

15

Use of TMEDA-Et₂O instead of THF gave almost the same results.