TETRAHEDRON LETTERS Tetrahedron Letters 43 (2002) 5587–5589 Pergamon New polymer anchored chiral amino oxazolines as effective catalysts for enantioselective addition of diethylzinc to aldehydes Nadim S. Shaikh, Vishnu H. Deshpande* and Ashutosh V. Bedekar* Division of Organic Chemistry: Technology, National Chemical Laboratory, Pune 411008, India Received 2 April 2002; revised 5 June 2002; accepted 13 June 2002 Abstract—The application of a new type of polymer anchored chiral amino-oxazolinyl ligand as catalyst for the enantioselective addition of diethylzinc to aldehydes is reported. The catalyst is effective at a low ligand concentration and can be reused with minimal loss of activity. © 2002 Published by Elsevier Science Ltd. Several chiral ligands have proven extremely successful in catalytic enantioselective nucleophilic addition of dialkylzinc to aldehydes, 1 probably the most widely studied asymmetric carboncarbon bond forming reac- tion. Since the pioneering work of Noyori 2,3 using (-)-3-exo -dimethylaminoisoborneol for highly enan- tioselective catalytic addition of dimethylzinc to ben- zaldehyde, a large number of different types of chiral amino alcohols have been prepared and utilized as catalysts for this reaction. In comparison a very few successful examples of diamine catalysts 1c,4 have been reported for this conversion. Optically active catalysts with an oxazoline moiety have a unique place in the rapidly growing field of enantioselective conversions mainly due to their simple preparation from natural amino acids and suitable structural features. Ferrocene- based oxazolines 5 as well as other oxazolinyl catalysts 6 have been found to be effective in catalyzing the asym- metric addition of diethylzinc and diarylzinc 5d to vari- ous aldehydes. The strategy of attaching a chiral ligand onto a polymer has been widely used to prepare heterogeneous, immo- bilized catalysts for enantioselective conversions. 7 This approach is advantageous compared to the classical homogeneous version due to: (1) the ease of separation of the expensive chiral catalyst from the reaction sys- tem, and hence the possibility of reutilizing the catalyst for successive reactions, (2) convenient operation in flow reactors or flow membrane reactors for continuous production and (3) for the development of environmen- tally safe processes for the production of fine chemicals. Reports of several polymer-supported chiral ligands have been documented 1c,8 for the specific reaction of the catalytic asymmetric addition of dialkylzinc to aldehydes. The chelation of diethylzinc with ligands is crucial in increasing its nucleophilicity and, hence, its reactivity towards aldehydes. The chiral environment of the lig- and is responsible for determining the stereochemical outcome of the addition reaction. A few chiral hydroxy-oxazolines have been used as ligands in this reaction but we believe that amino-oxazolines could be better chelates due to the higher nucleophilicity of the amino group compared to alcohols. This enhanced chelating ability may help to overcome the problem of low reactivity of heterogeneous polymer-supported chi- ral ligands. With this concept, we have prepared a new type of polymer-anchored oxazoline and wish to present our results of screening as catalysts in the addition of diethylzinc to aldehydes. Scheme 1. * Corresponding authors. Present address (A.V.B.): Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute (CSMCRI), G.B. Road, Bhavnagar 364002, India; E-mail: vhdesh@dalton.ncl.res.in; avbedekar@yahoo.co.in 0040-4039/02/$ - see front matter © 2002 Published by Elsevier Science Ltd. PII:S0040-4039(02)01139-5