Catalytic Synthesis of Pyrano- and Furoquinolines Using Nano Silica Chromic Acid at Room Temperature

Table 5

The effectiveness of varities catalysts in the synthesis of pyranoquinolines (Table 1, Entry 4, compounds 4a and 5a) in THF as solvent.

Entry	Catalyst	^aYield (%)	Time (min)	^bProduct ratio; 4a : 5a (trans : cis)
1	Nano SCA	94	65	90 : 10
2	ZnO	61	91	64 : 36
3	H2SO4	81.5	88	80 : 20
4	Bi(OTf)3	77	92	66 : 34
5	Yb(OTf)3	78	96	61 : 39
6	Free	36.5	145	53 : 47

aIsolated yield. ^bIsomers were separated by column chromatography.
^bRatio of the product was determined from the crude ¹H NMR spectra.