Trimethylpyrylium Tetrafluoroborate

Record the yield, melting point, and H NMR spectrum of the product. 

---

Treatment of [W(N2)2(PMe2Ph)4] with HCl under CO afforded [W (NNH2)(CO)(PMe2Ph2)Cl2], which reacted with 2,4,6-trimethylpyrylium tetrafluoroborate in the presence of HCl giving the (l-pyridino)imino complex [W (NNC5H2Me3)(CO)(PMe2Ph)2]+. 

Trimethylpyrylium tetrafluoroborate (X) serves as reactant in the following transformations ... 

The NMR spectrum of 2,4,6-trimethylpyrylium tetrafluoroborate contains two closely spaced singlets in a ratio very close to 1 4. Explain why there are two fluorine signals and why the ratio is 1 4. 

A valuable development of this method has been the use of an alcohol or alkyl halide as an in situ source of the alkene. This particular approach provides a very convenient synthesis of 2,4,6-trimethylpyrylium <73OSC(5)li06) and 2,3,4,6-tetramethyIpyrylium salts (820PP31). It is noteworthy that the trifluoromethanesulfonate and tetrafluoroborate derivatives of the former are non-explosive, unlike the perchlorate, and the sulfoacetate has much to commend it (820PP39). 

The diacetylation of isobutene (6, R = Me) introduced either as gas, or as tert-butanol with Bronsted acids such as perchloric, tetrafluoroboric, trifluoromethanesulfonic or sulfoacetic acids) or as tert-h Ay chloride with Lewis acids such as AICI3 or FeCla proceeds via the monoacetylation products, mesityl and isomesityl oxides (10 and 9, respectively), and yields the corresponding 2,4,6-trimethylpyrylium salts (11, R = Me). 

Detailed procedures were published for synthesizing 2,4,6-trimethylpyrylium perchlorate, tetrafluoroborate, triflate, and sulfoacetate. Being salts, these compounds are insoluble in ether and are therefore easily purified from side products such as mesityl oxide, so that yields are at least 50-60%. With propene (6, R = H) the yield in 2,6-dimethylpyiylium perchlorate is lower than with isobutene. ... 

---