Highly selective monoetherification of symmetrical diols catalysed by metallic sulfate supported on silica gel

Abstract

Several symmetrical primary and secondary diols from C, t o C,, have been protected in high selectivity by tetrahydropyranyl ether formation catalysed by metallic sulfates supported on silica gel. This selective etherification is simple and practical. The selectivity of monoether formation depends upon the composition and the volume of solvents. The selectivity can be explained by preferential adsorption of diols to monoethers and the formation of thin liquid films of diols on the surface of catalysts caused by the limited dissolution of the diols in DH P-hexane mixtures.

Convenient tetrahydropyranylation of alcohols and phenols by catalytic ferric sulfate hydrate (Fe2(SO4)3·xH2O)

“…Meanwhile, the selective protection of one of two identical hydroxyl groups in a symmetrical molecule is relatively limited. Previously, the selective monotetrahydropyranylation was achieved through control of the volume of solvents and usage of metallic sulfates supported on silica gel (13). Recently, I 2 under microwave-assisted (14), ionic liquid ([CnMIM][AlCl 4 ]) (15), and LiOTf in ClCH 2 CH 2 Cl at reflux (9) have been reported for this transformation.…”

Kinetic and Thermodynamic Studies of the Urethane Reaction Based on 1,3-diazetidine-2,4-dione and 4-(Tetrahydro-Pyran-2-yloxy)-butan-1-ol

“…The product was purified by filtering the reaction mixture through a short column of silica gel (EtOAc:hexane = 1:4). [24,25] …”

Selective Monoprotection of Symmetrical Diols in a Flow Reactor

“…In order to overcome this limitation, the selective monoprotection of symmetrical diols has been typically performed using an excess of diol. Moreover, catalysts with a relatively small catalytic surface such as ion-exchange resins (namely, Amberlite IR-120 [21], Amberlist H-15 [22], Rellex 425 [23], Dowex 50 [24], and Nafion-H [25]), iodine [26], ZrO 2 -pillared clay [27], zinc chloride [28], and aqueous acids [29] have been reported to be effective for selective monotetrahydropyranylation.…”

“…The residue was purified by column chromatography on silica gel to give 4-((tetrahydro-2H-pyran-2-yl)oxy)butan-1-ol (2) and 1,4-bis((tetrahydro-2H-pyran-2-yl)oxy)butane (3)[21]. Unreacted 1 was found in the aqueous layer and was quantified (mmol) by the difference between the amount of starting substrate (11.1 mmol) and the amount of product (mmol).4-((Tetrahydro-2H-pyran-2-yl)oxy)butan-1-ol (2) NMR (500 MHz, CDCl 3 ): δ 4.60 (dd, J = 2.9, 4.0 Hz, 1H), 3.86 (ddd, J = 3.5, 8.0, 11.4 Hz, 1H), 3.80 (dt, J = 4.9, 11.4 Hz, 1H), 3.67 (brs, 2H), 3.51 (dt, J = 5.4, 10.9 Hz, 1H), 3.43 (dt, J = 5.7, 9.8 Hz, 1H), 2.19 (brs, 1H), 1.81 (m, 1H), 1.75 -1.66 (m, 5H), 1.61 -1.50 (m, 4H); 13 C NMR (125 MHz, CDCl 3 ): δ 99.0, 67.6, 62.8, 62.5, 30.7, 30.2, 26.7, 25.5, 19.6.…”