An Efficient and Chemoselective Cleavage of Prenyl Ethers with DDQ

Abstract

The prenyl (Pre) protecting group for hydroxyl functions is readily removed at room temperature with DDQ in dichlor­omethane-water (9:1). The reaction conditions are compatible with the presence of other ethereal functionalities such as acetonides, allyl, benzyl, TBS, TBDPS groups. We have also shown that deprotection of prenyl ethers using a catalytic amount of DDQ in the presence of 3 equivalents of Mn(OAc)₃ is a good alternative for the use of a stoichiometric amount of DDQ, albeit the reaction time being longer.

DDQ - cleavage - protecting groups - ethers - oxidation

References

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5

General Experimental Procedure for the Cleavage of Prenyl Ethers: To a stirred solution of the prenyl ether (1 mmol) dissolved in 9 mL of CH₂Cl₂ were added water and DDQ (0.272 g; 1.2 equiv). Reaction progress was monitored by TLC. Upon consumption of the prenyl ether, 2,3-dichloro-5,6-dicyanohydroquinone was filtered. To the filtrate was added a sat. NaHCO₃ solution and the aq phase was extracted twice with CH₂Cl₂. Drying over Na₂SO₄, filtering, evaporation to dryness gave a material that was purified by flash column chromatography using petroleum ether-ether as eluent (2:1 ratio for compounds 2a,b, 2f and 2h-j; 1:2 for 2d, 2g and 2k; 4:1 for 2e and ether for 2c.

6

Compounds 2a-g and 2i-k exhibited physical and spectral data in accordance with those described in the literature. New compound 2h gave spectroscopic and analytical data in agreement with the assigned structure. ¹H NMR (CDCl₃, 200 MHz): δ = 1.28-1.72 (6 H, m), 2.55 (1 H, s, OH), 3.39 (t, 2 H, J = 6.3 Hz, CH₂OAll), 3.58 (t, 2 H, J = 6.4 Hz, CH₂OH), 3.93 (dt, 2 H, J = 5.6 and 1.4 Hz, CH₂-CH=CH₂), 5.12 (brd, 1 H, J = 10 Hz, CH=CH₂), 5.22 (dq, 1 H, J = 17 Hz and 1.5 Hz, CH=CH₂), 5.88 (ddd, 1 H, J = 5.6, 10 and 17 Hz, CH=CH₂); ¹³C NMR (CDCl₃, 50.3 MHz): δ = 22.4, 29.4, 32.4, 62.5, 70.3, 71.8, 116.8, 134.9. Anal. Calcd for C₈H₁₆O₂: C, 66.63; H, 11.18. Found: C, 66.55; H, 11.22.

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9 This α,β-unsaturated aldehyde was isolated and has spectroscopic data in accord with those described in the literature: Vani PVSN. Chida AS. Srinivasan R. Chandrasekharam M. Singh AK. Synth. Commun.  2001,  31:  219