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

Table 3

The effectiveness of varities solvents in the synthesis of pyranoquinolines (Table 1, Entry 4, compounds 4a and 5a) using nano silica chromic acid (nano-SCA) catalyst.

Entry	Solvent	Time (min)	^aYield (%)	^bProduct ratio 4a : 5a (trans:cis)
1	THF	65	94	90 : 10
2	CCl4	91	72.5	81 : 19
3	CHCl3	74	69	80 : 20
4	CH2Cl2	69	73	73 : 27
5	DMF	115	68	65 : 35
6	DMSO	125	52	62 : 38
7	CH3CN	76	58	67 : 33
8	C6H5CH3	87	70	69 : 31
9	Free	95	59	62 : 28
10	Pyridine	110	61.5	66 : 34

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