Ease to Challenges in Achieving Successful Synthesized Schiff Base, Chirality, and Application as Antibacterial Agent

Table 1

Asymmetric nitro aldol (Henry) reaction between nitromethane and p-nitrobenzaldehyde catalyzed by chiral Schiff base [22].

Entry	Cat.	M(OTf)2	Time (h)	Yield^b (%)	e.e^c (%)	Config.^d
1	3	Cu(OTf)2	40	56	44	(R)
2	3	Zn(OTf)2	40	62	8	(S)
3	4	Cu(OTf)2	40	45	30	(S)
4	4	Zn(OTf)2	40	57	18	(S)
5	5	Cu(OTf)2	40	56	47	(R)
6	5	Zn(OTf)2	40	63	11	(S)
7	6	Cu(OTf)2	40	54	27	(S)
8	6	Zn(OTf)2	40	64	17	(S)

^aAll reactions were performed on a 0.2 mmol scale of 4-nitrobenzaldehyde in the mixture of 0.8 ml of ethanol and 0.6 ml of nitromethane. ^bAfter purification with thin layer chromatography (TLC), ethyl acetate/petroleum ether (30 : 70) R_f: 0.36, while literature gave 0.34. ^cDetermined by chiral high-performance liquid chromatography (HPLC) using an OD column. ^dDetermined by comparing HPLC elution order of the enantiomers with a genuine sample according to the literature and that by HP chiral detectors [22]. OTf is the triflate group, identified by the systematic name trifluoromethanesulfonate.