DOI: 10.1002/adsc.200606125 New Recoverable Poly(ethylene glycol)-Supported C 1 -Diamino- oligothiophene Ligands for Palladium-Promoted Asymmetric Allylic Alkylation (AAA) Reactions Marco Bandini, a, * Maurizio Benaglia, b, * Tommaso Quinto, a Simona Tommasi, a and Achille Umani-Ronchi a a Dipartimento di Chimica “G. Ciamician”, Università di Bologna, via Selmi 2, 40126, Bologna, Italy Fax: (+ 39)-051-209-9456; e-mail: marco.bandini@unibo.it b Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy Fax: (+ 39)-02-5031-4159; e-mail: maurizio.benaglia@unimi.it Received: March 22, 2006; Accepted: June 2, 2006 Dedicated to Professor Mauro Cinquini on occasion of his 65 th birthday. Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/. Abstract: A new class of chiral C 1 -symmetrical di- amino-oligothiophene ligands easy-grafted on a soluble polymeric support (MeOPEG 5000 ) is de- scribed. The diamines were found to be effective promoting agents for the [Pd(0)]-catalysed asym- metric allylic alkylation (AAA) of dimethyl malo- nate in high yields and excellent enantioselectivity (ee up to 99%). The supported chiral ligand was readily recovered by precipitation and filtration was recycled up to three times without an appreciable loss in activity. The recycle of the organometallic catalytic system was also investigated. Keywords: asymmetric synthesis; palladium; PEG; supported catalysts; thiophene The design and application of new chiral catalysts for the synthesis of enantiomerically enriched molecules have gained an ever-growing attention in the field of the chemical research over the last three decades. [1,2] In this context, although the major developments in this field have mainly concerned processes in which a catalytic stereoselective system is solubilised in the re- action media, homogeneous catalysis suffers from a limited use on an industrial scale, because of the lack of easy separation and recycling of the undesired components of the final product and environmental concerns. [3] The grafting of chiral ligands as well as or- ganometallic complexes onto solid insoluble supports (heterogeneous catalysis) [4] is commonly accepted as a promising route for the diffusion of asymmetric cat- alytic transformations at the industry level. In many instances, the main goal of the immobilisa- tion was the simplification of the reaction work-up, the separation of the product being simpler in the case of a supported rather than a non-supported cata- lyst. However, with the continuing discovery of more and more sophisticated chiral catalytic species, also recovery and recycling will surely become an impor- tant issue in justifying catalyst immobilisation. Immo- bilisation is obviously convenient if the catalyst is ex- pensive, or has been obtained after a complex synthe- sis, or is employed in a relatively large amount. A cat- alyst)s instability can be another reason for immobili- sation. Chiral catalysts do exist that slowly decompose under the reaction conditions and release trace amounts of by-products that must be separated from the products. If decomposition is slow and the catalyst is very chemically active, this phenomenon does not markedly affect the efficiency of the catalyst and its recycling, but product purification remains a problem. Last but definitely not least, immobilisation of a chiral catalyst can be used in a combinatorial ap- proach to facilitate the process of catalyst discovery and/or optimisation. Despite this interest, the use of chiral catalysts im- mobilised on heterogeneous supports is often charac- terised by some problems; for example, they com- monly promote the reaction with a chemical and ste- reochemical efficiency lower than those of the non- supported catalytic systems. The immobilisation of an organometallic catalyst, generally obtained by anchor- ing an organic ligand on the support followed by metal addition, may also suffer from the serious draw- back of metal leaching. To overcome these limitations, soluble organic polymers were introduced as a valuable alternative; Adv.Synth.Catal. 2006, 348, 1521–1527 # 2006 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 1521 COMMUNICATIONS