High-Speed Reduction of Triarylpyrylium Salts Using Zn(BH₄)₂/SiO₂ as an Efficient and Regiospecific Reducing Reagent

Table 1

Comparing the ability of different hydride donors for reduction of triphenylpyrylium salts in various solvent.

Entry	Reducing reagent	Solvent	Time	Results
1	NaBH4	THF	1 h	Dienone and 4H-pyran
2	BER	THF	4 h	Dienone and 4H-pyran
3	SBER	CH3OH	4 h	Dienone and 4H-pyran
4	Zn (BH4)2	THF	Imm.	Dienone
5	Zn (BH4)2/SiO2	THF	5 min	Dienone

Imm: immediately (1 min).