Abstract
A potent, eco-friendly approach for converting 2,6-arylpiperidin-4-ones into their corresponding oximes in the presence of hydroxylamine hydrochloride and catalysed by nanosize sulfated titania (TiO2/SO42-) solid superacid was developed. Sol-gel method was employed to synthesize the catalyst and confirmed standard characterization techniques viz., by FT-IR, XRD, TEM, SEM, and EDS analysis. After adding 0.05 g of catalyst, the reaction was carried out under stirring in an oil bath at 130°C for 3-7 min under solvent-free conditions. This approach has advantages like catalyst recyclability, high yields, shorter reaction time, and simple work-up. Additionally, the catalyst TiO2/SO42- exhibited good stability, recoverability, and reusability for five consecutive runs without tremendous loss in its catalytic activity. The compounds 3a-o were characterised by IR, 1H and 13C NMR spectral analysis. The coupling constant values in NMR results suggested that the compounds 3a-o exhibit chair conformation with equatorial orientations with all the substituents. This is in agreement with the X-ray crystallography of 3c, confirming that the chair conformation of =N-OH group is syn to C-5 and anti to benzyl group at C-3 and hence if forms more stable (E)-configuration of the oxime 3c.
Graphical Abstract
[http://dx.doi.org/10.1039/C1RA00807B]
[http://dx.doi.org/10.1039/C2CC35663E] [PMID: 23212208]
[http://dx.doi.org/10.1186/2193-8865-3-25]
[http://dx.doi.org/10.1002/slct.202104505]
[http://dx.doi.org/10.1007/s00706-015-1533-5]
[http://dx.doi.org/10.3390/catal11121542]
[http://dx.doi.org/10.1016/j.mcat.2018.05.009]
[http://dx.doi.org/10.1039/C4NJ00494A]
[http://dx.doi.org/10.1021/acs.iecr.6b02619]
[http://dx.doi.org/10.1021/am900437u] [PMID: 20356115]
[http://dx.doi.org/10.1016/0079-6786(88)90005-2]
[http://dx.doi.org/10.1016/j.cdc.2020.100565]
[http://dx.doi.org/10.1016/j.cdc.2020.100589]
[http://dx.doi.org/10.1002/0471220574]
[http://dx.doi.org/10.1055/s-1996-4325]
[http://dx.doi.org/10.3998/ark.5550190.0007.204]
[http://dx.doi.org/10.1021/jo00905a019]
[http://dx.doi.org/10.1021/jo9614755] [PMID: 11667870]
[http://dx.doi.org/10.1055/s-1996-5666]
[http://dx.doi.org/10.1351/pac200375010019]
[http://dx.doi.org/10.1055/s-1983-30409]
[http://dx.doi.org/10.1021/jo070297k] [PMID: 17480096]
[http://dx.doi.org/10.1021/ja053441x] [PMID: 16089442]
[http://dx.doi.org/10.1002/(SICI)1521-3773(19981116)37:21<2975:AID-ANIE2975>3.0.CO;2-A] [PMID: 29711128]
[http://dx.doi.org/10.1021/cr940089p] [PMID: 11749257]
[http://dx.doi.org/10.1039/b107356g]
[http://dx.doi.org/10.1016/S0040-4039(01)01851-2]
[http://dx.doi.org/10.1007/s00706-005-0427-3]
[http://dx.doi.org/10.1016/j.apcata.2007.04.025]
[http://dx.doi.org/10.1016/j.ultsonch.2008.09.003] [PMID: 18977162]
[http://dx.doi.org/10.1016/j.tetlet.2011.07.015]
[http://dx.doi.org/10.2174/2211544712666230103163911]
[http://dx.doi.org/10.1016/j.bmcl.2008.10.045] [PMID: 18952418]
[http://dx.doi.org/10.1021/jm000038m] [PMID: 10956199]
[http://dx.doi.org/10.1016/j.ejmech.2006.02.005] [PMID: 16600438]
[http://dx.doi.org/10.1016/j.ejmech.2006.12.005] [PMID: 17275965]
[http://dx.doi.org/10.1002/prac.19853270418]
[http://dx.doi.org/10.1016/j.ejmech.2008.03.031] [PMID: 18485539]
[http://dx.doi.org/10.1016/j.ejmech.2014.05.080] [PMID: 24929294]
[http://dx.doi.org/10.2174/2211352517666190405155505]
[http://dx.doi.org/10.1016/j.jep.2009.02.033] [PMID: 19429336]
[http://dx.doi.org/10.1248/bpb.26.188] [PMID: 12576678]
[http://dx.doi.org/10.1016/j.bmc.2018.04.056] [PMID: 29729988]
[http://dx.doi.org/10.1002/jhet.3040]
[http://dx.doi.org/10.1021/jm00329a015] [PMID: 5867943]
[http://dx.doi.org/10.1016/j.ejmech.2005.10.014] [PMID: 16380194]
[http://dx.doi.org/10.1081/CLT-120015840] [PMID: 12475193]
[http://dx.doi.org/10.1038/s41598-020-57794-1] [PMID: 31969653]
[http://dx.doi.org/10.1021/ja01511a053]
[http://dx.doi.org/10.1055/s-2000-6752]
[http://dx.doi.org/10.3184/030823400103165545]
[http://dx.doi.org/10.1016/0926-860X(91)85009-M]
[http://dx.doi.org/10.1002/mrc.1260240409]
[http://dx.doi.org/10.1021/ja00429a007]
[http://dx.doi.org/10.1107/S1600536808016449] [PMID: 21202850]
[http://dx.doi.org/10.1246/bcsj.20120221]
[http://dx.doi.org/10.1016/j.tetlet.2012.06.024]
[http://dx.doi.org/10.1016/j.molstruc.2020.128810]