In Situ Generation Of Formaldehyde And Triphenylphosphine From (Hydroxymethyl) Triphenylphosphonium And Its Application In Wittig Olefination

Formaldehyde is the simplest and the most common aldehyde in nature, it is widely used in chemical synthesis, pharmaceutical synthesis and other industrial areas. But formaldehyde is a toxic gas, it is flammable and corrosive. So chemists often use formalin or paraformaldehyde as the substitute of formaldehyde to participate chemical reactions. This not only needs greatly excessive formaldehyde, but also brings serious pollution and limit the application of formaldehyde.We found that(hydroxymethyl)triphenylphosphonium tetrafluoroborate, with K2CO3 in acetronitrile at room temperature can produce formaldehyde, and we used this method in Wittig Olefination. Treatment of(hydroxymethyl) triphenylphosphonium tetrafluoroborate and benzylic or allylic halides with K2CO3 in acetronitrile at room temperature affords terminal alkenes in 61-89% yields.This method has the following advantages:(1)(hydroxymethyl)triphenyl phosphonium is stable and easy-to-handle;(2) equimolar of(hydroxymethyl)triphenyl phosphonium is used in contrast to a large excess of formalin or paraformaldehyde; and(3) the reaction allows in situ generation of formaldehyde with concomitant release of triphenylphophine which is trapped by benzylic or allylic halides to generate phosphonium salts. So phosphonium salts do not need to prepare in advance.