Triethylsilane → Benzo[b]thiophene-5-ol, 2,3-dihydro-

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Reaction Conditions

Reaction Steps

To a warm mixture of 5-hydroxy benzothiophene (10.0 g, 66.58 mmole) (Fieser & Kennelly, J. Amer. Chem. Soc., Vol. 57, pp 1611-1614, (1935)) in 100 mL TFA was added triethylsilane (19.35 g, 166.45 mmole, 2.5 eq.) The resulting purple solution was heated to 55° C. under N2 overnight. After 24 hours a sample removed for NMR analysis showed the reaction to be about 80% complete. Much of the original purple color had also been discharged at this point. An additional portion of triethylsilane (3.9 g, 0.5 eq) was added and the heating was continued for another 24 hours. NMR analysis at the 48 hour time point showed virtually no change from the 24 hour time point. Most of the TFA was distilled off under reduced pressure (40 mmHg). The residue was taken up in 300 mL H2O and rendered alkaline (pH=10 to pH paper) with 5N NaOH and washed with ether (2×100 mL). The aqueous phase was acidfied with 2N HCI and extracted with ether (3×200 mL). The combined organic extracts were washed with sodium bicarbonate (1×100 mL), H2O (1×100 mL) and brine (1×100 mL). Drying over Na2SO4 and concentration gave 4.7 g (46.5%) gray solids. Purification by preparative chromatography on a Waters 500A prep HPLC using 2 columns and 90/10 vol/vol hexane/EtOAc to elute afforded 3.0 g (30%) pure material (single spot by TLC analysis) mp 87°-89° C.

Provenance & Evidence