In this presentation, we report on our development of a new class of phase transfer agents that rapidly fluorinate hindered aryl and alkyl silicon ethers relative to existing techniques. This new approach was developed for use in positron emission tomography (PET). Applications in the selective removal of silicon-based protecting groups are also envisioned. To accomplish this rate acceleration, we have developed crown ether nucleophilic catalysts (CENCs) that are capable of serving both as phase transfer agents and also catalyzing the fluorination of silicon most likely by stabilizing its hypervalent intermediate. In our development, a series catalysts have been prepared containing different spacer units connecting the crown ether to the hydroxyl group, which is believed to act as the initial nucleophile to attack silicon in this system. In addition to hydroxyl, the pendant functional group in these CENCs has also been varied to include a variety of hydrogen bond donors and acceptors. The results of this catalyst SAR study along with studies involving variations of the silicon substrate will be discussed especially as they relate to our emerging mechanistic explanation for the observed rate enhancement.

Crown ether nucleophilic catalysts (CENCs) for the ultrafast fluorination of silicon

251st National Meeting (2016)

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