Abstract
A simple and efficient method for the conversion of carbonyl compounds to oxathioacetals and dithioacetals by using polyphosphoric acid supported on silica gel (PPA/SiO2 ) as an acid catalyst have been developed. PPA/SiO2 is easily recovered from the reaction mixture and reused without a decrease in catalytic activity.
Key words
oxathioacetals - dithioacetals - protecting groups - polyphsphoric acid - silica gel
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The Preparation of PPA/SiO
2
: PPA (2.1 g) was charged in the round-bottom flask, and CHCl3 (100 mL) was added. After the mixture was stirred at 50 ºC for 1 h, SiO2 [Wakogel C-200 (Wako Pure Chemical Ind. Ltd.), 4.9 g] was added to the solution, and the mixture was stirred for another 1 h. The CHCl3 was removed with rotary evaporator and the resulting solid was dried in vacuo at r.t. for 3 h.
19 Used PPA/SiO2 was regenerated as follows: PPA/SiO2 was recovered by filtration from the reaction mixture, and then it was put in the 50 mL round-bottom flask and dried in vacuo at 100 °C for 2 h.