Enantioselective desymmetrization of meso-epoxides with anilines catalyzed by polymeric and monomeric Ti(IV) salen complexes |
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Authors: | Kureshy Rukhsana I Kumar Manish Agrawal Santosh Khan Noor-Ul H Dangi Balchand Abdi Sayed H R Bajaj Hari C |
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Affiliation: | Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (CSMCRI), Council of Scientific and Industrial Research (CSIR), G. B. Marg, Bhavnagar, Gujarat, India. rukhsana93@yahoo.co.in |
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Abstract: | The active catalysts for the enantioselective ring opening (ARO) of meso-stilbene oxide, cis-butene oxide, cyclohexene oxide, cyclopentene oxide, and cyclooctene oxide with various substituted anilines were generated in situ by the reaction of Ti(O(i)Pr)(4) with poly-[(R,R)-N,N'-bis-{3-(1,1-dimethylethyl)-5-methylene salicylidene} cyclohexane-1,2-diamine]-1 and (1R,2R)-N,N'-bis[3,5-di(tert-butyl)salicylidene] cyclohexane-1,2-diamine-2. These catalysts in the presence of nonracemic imine as an additive provided β-amino alcohol in excellent yield (99%) and chiral purity (enantiomeric excess (ee) up to 99%) for the ARO of meso-stilbene oxide with aniline. The same protocol was less effective for the ARO of cyclic epoxides; however, when triphenylphosphine was used as an additive, there was a significant improvement in catalyst performance for the ARO of cyclohexene oxide (yield, 85-90%; ee, 63-67%). Both in situ generated polymeric and monomeric catalysts performed in a similar manner except that the polymeric catalyst Ti(IV)-1 was more active and recycled several times with retention of enantioselectivity when compared with the monomeric catalyst Ti(IV)-2, which was nonrecyclable. |
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