کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5220231 | 1383381 | 2012 | 9 صفحه PDF | دانلود رایگان |
Chiral dimeric Mn(III) salen complex with 1R, 2R-(â)-diaminocyclohexane collar was immobilized on short channel large pore sized silica through a long linker of {(CH2)3-NH-melamine-piperazine} to investigate its performance in enantioselective epoxidation of chromenes, indene, styrene and cis β-methyl styrene in the presence of pyridine N-oxide (PyNO) as an axial base using aqueous NaOCl as an oxidant at 0 °C. The immobilized catalyst system showed high turnover frequency (TOF) and enantioselectivity for the smaller and bulkier alkenes like styrene, indene, 2,2-dimethylchromene and 6-cyano-2,2-dimethylchromene (ee up to 98%). These results are the best reported for heterogeneous catalyst under biphasic reaction conditions and were comparable to the dimeric Mn(III) salen system under homogeneous condition. The performance of the immobilized catalyst was retained for six reuse experiments. This protocol was extended to the synthesis of an antihypertensive drug (S)-Levchromakalim (ee 98%) at 1 g level.
Journal: Tetrahedron - Volume 68, Issue 31, 5 August 2012, Pages 6314-6322