A stable reagent for synthesis of conjugated enynes from enals

Synlett

Volumn , Issue 18, 2009, Pages 3037-3039

  Zhang, Yan ^a   Li, Yun ^a   Wu, Yikang ^a  

^a SHANGHAI INSTITUTE OF ORGANIC CHEMISTRY   (China)

Author keywords

Alkynes; Carbenes; Elimination; Phosphates; Wittig reactions

Indexed keywords

ALKYNE DERIVATIVE; CARBENOID; ENAL DERIVATIVE; ENYNE DERIVATIVE; OHIRA BESTMANN REAGENT; PHOSPHATE; REAGENT; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL STRUCTURE; CONJUGATION; CONTROLLED STUDY; SHELF LIFE; SYNTHESIS;

EID: 71949131569     PISSN: 09365214     EISSN: 14372096     Source Type: Journal    
DOI: 10.1055/s-0029-1218010     Document Type: Article

References (16)

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6. (f) Gilbert J C., Weerasooriya U, J. Org. Chem. 1982 74 1837
7. (g) A referee informed us that Maehr et al. recently reported that 1 is more stable than previously believed and could be stored in refrigerators for years, see:, Maehr H, Uskokovic M R., Schaffner C P., Synth. Commun. 2009 39 299
8. (a) Ohira S, Synth. Commun. 1989 19 561.
9. (b) Roth G J., Liepold B, Müller S, Bestmann H J., Synthesis 2004 59.
10. (c) Müller S, Liepold B, Roth G J., Bestmann H J., Synlett 1996 521
11. Teulade M.-P, Savignac P, Aboujaoude E E., Collignon N, J. Organomet. Chem. 1986 312 283
12. Ditrich K, Hoffmann R W., Tetrahedron Lett. 1985 26 6325
13. Synthesis of Compound 3 n-BuLi (2.5 M in hexanes, 15.76 mL, 39.4 mmol) was added to a solution of 4 (6.0 g, 39.4 mmol) in dry THF (40 mL) stirred at ?78 ?C under argon. The mixture was stirred at the same temperature for 1 h before a solution of g-butyrolactone (2.15 mL, 28 mmol) in dry THF (5 mL) was introduced. The originally slightly cloudy mixture now became clear. The bath temperature was allowed to rise slowly to ambient temperature. The stirring was then continued for another 2 h. After that, the bath was re-cooled to ?78 ?C before a solution of LDA (28 mmol, freshly prepared from 4.0 mL of i-Pr2NH and 11.2 mL of 2.5 M n-BuLi) in dry THF (20 mL) was introduced. The mixture was stirred for 30 min. TESCl (9.4 mL, 56 mmol) was then added. The mixture was stirred at ambient temperature overnight. Aq sat. NH4Cl was added, followed by EtOAc. The phases were separated. The organic layer was washed with H2O and brine before being dried over anhyd Na2SO4. Removal of the solvent by rotary evaporation and column chromatography (PE?EtOAc = 1:1 to 1:2) on silica gel gave the intermediate acyl phosphate 4b as a colorless oil (8.57 g, 87% from 4). A portion of this oil (4b, 7.596 g, 21.5 mmol) was dissolved in THF (30 mL). With cooling (ice-water bath) and stirring, powdered K2CO3 (3.3 g, 23.9 mmol) was added, followed by TsN3 (4.7 g, 23.9 mmol). The mixture was stirred at the bath temperature for 2 h and then at ambient temperature overnight before being diluted with Et2O, washed with aqsat. NH4Cl, and dried over anhyd Na2SO4. Removal of the solvent by rotary evaporation and column chromatography (PE?EtOAc = 3:1) on silica gel gave 5 as a colorless oil (5.53 g, 68% from the intermediate acyl phosphate). 1H NMR (300 MHz, CDCl3): d = 4.25?4.08 (m, 4 H), 3.65 (t, J = 6.0 Hz, 2 H), 2.66 (t, J = 7.3 Hz, 2 H), 1.86 (quin, J = 6.6 Hz, 2 H), 1.39 (t, J = 7.1 Hz, 6 H), 0.96 (t, J = 7.9 Hz, 9 H), 0.59 (q, J = 7.9 Hz, 6 H). FT-IR (film): 3412, 2955, 2123, 1659, 1253, 1019, 977, 742, 589 cm?1. ESI-MS: m/z = 401.1 [M + Na]+. ESI-HRMS: m/z calcd for C15H31N2O5PSiNa: 401.1632 [M + Na]+; found: 401.1634. AcOH (11 mL) was added slowly to a solution of 5 (2.5 g, 6.76 mmol) in THF?H2O (20 mL, 1:1 v/v) stirred in an icewater bath. After completion of the addition, the mixture was stirred at the same temperature for another 10 min. Na2CO3 was carefully added to neutralize the acid. The mixture was extracted with EtOAc. The combined organic layers were concentrated on a rotary evaporator. The residue was chromatographed (PE?EtOAc = 1:2) on silica gel to give 3 as yellowish oil (1.25 g, 4.73 mmol, 70%). 1H NMR (300 MHz, CDCl3): d = 4.30?4.10 (m, 4 H), 3.66 (t, J = 6.1 Hz, 2 H), 2.72 (t, J = 6.9 Hz, 2 H), 2.10?1.90 (brs, 1 H), 1.92 (quin, J = 6.5 Hz, 2 H), 1.39 (t, J = 7.0 Hz, 6 H). 13C NMR (75 MHz, CDCl3): d = 193.2 (d, JC?P = 14 Hz), 63.5 (d, JC?P = 6 Hz), 61.3, 35.9, 27.1, 15.9 (d, JC?P = 7 Hz). FT-IR (film): 3443, 2986, 2118, 1656, 1369, 1251, 1032, 977, 593 cm?1. ESI-MS: m/z = 287.0 [M + Na]+. ESI-HRMS: m/z calcd for C9H17N2O5PNa: 287.0767 [M + Na]+; found: 287.0769.
14. For the reaction of diakyl methylphosphate with -butyrolactone, see:, Ditrich K, Hoffmann R W., Tetrahedron Lett. 1985 26 6325
15. In the absence of the crown ether, the reaction was very slow; most of the starting enal (except 6a) remained unchanged after 4?5 h at ?78 ?C along with some uncharacterized intermediates and small amounts of the desired enyne.
16. General Procedure for the Conversion of 6 into 7 NaHMDS (2.0 M in THF, 55 mL, 0.11 mmol) was added to a solution of 3 (29 mg, 0.11 mmol) in dry THF (1.0 mL) stirred at ?78 ?C under argon. The mixture was stirred at the same temperature for 30 min, when a solution of enal 6 (0.073 mmol) in dry THF (0.5 mL) was added slowly (the mixture darkened soon). 15-Crown-5 ether (22 mL, 0.11 mmol) was then added in one portion. The mixture was stirred at the same temperature for 1 h. Aq sat. NH4Cl was added, followed by Et2O. The phases were separated. The organic layer was dried over anhyd Na2SO4. Removal of the solvent by rotary evaporation and column chromatography on silica gel gave the corresponding 7.