FULL PAPER DOI: 10.1002/ejoc.200601081 Diastereoselective Cyclisation of N-Alkenylideneamines into 3,4-Dihydro-2H- pyrrol-1-ium Halides Daniela Schley [a] and Jürgen Liebscher* [a] Dedicated to Prof. Dr. Manfred Christl on the occasion of his 65th birthday Keywords: Diastereoselective cyclisation / Pyrrolin-1-ium salts / Pyrrolidines / Heterocycles / Synthetic methods A number of new chiral 2-(α-bromoalkyl)pyrrolinium salts and 2-(α-selenoalkyl)pyrrolidines were synthesized by the halocyclisation and selenocyclisation, respectively, of N-(alk- enylidene)alkylamines and subsequent reduction. These cy- clisations were implemented in a diastereomeric fashion for the first time. Substrate control (starting imines possessing chirality in the N-alkyl or the N-alkenyl substituent) and re- Introduction The asymmetric functionalisation of olefins is an impor- tant goal in synthetic organic chemistry. Thus, highly stereoselective epoxidations, dihydroxylations and hydro- borations were developed. The addition of electrophiles to C=C bonds can also be combined with an intramolecular nucleophilic attack by ring formation, when alkenes with additional nucleophilic sites (O, S or N) are used as sub- strates. This electrophile-induced cyclisation is a versatile strategy for the construction of heterocycles. The halolac- tonisation, where unsaturated carboxylic acids are cyclised by a reaction with halogens to form lactones, is a well- known example of this type of reaction. Other common starting materials are unsaturated carboxylic acid deriva- tives, imines (Scheme 1), alcohols and amines. Halogens, N- halogenated succinimides, mercury(II) acetate, tert-butyl hydroperoxide [1] (Sharpless conditions) and organose- lenenyl halides [2–5] commonly serve as electrophiles. [6] The general mechanism of the electrophile-induced cyclisation of unsaturated imines is shown in Scheme 1. Chemo-, regio- and diastereoselectivity are important as- pects of such ring formations. Thus, the reaction of the elec- trophile can give just an addition to the double bond (e.g. to adduct 5) rather than undergoing a cyclisation to prod- ucts 6 or 7. On the other hand, in accordance with the Bal- dwin rules [7] the cyclisation can follow either the exo-trig or [a] Institut für Chemie, Humboldt-Universität Berlin, Brook-Taylor-Straße 2, 12489 Berlin, Germany E-mail: liebscher@chemie.hu-berlin.de Supporting information for this article is available on the WWW under http://www.eurjoc.org or from the author. Eur. J. Org. Chem. 2007, 2945–2957 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2945 agent control (chiral organoselenenyl bromides) were applied. Asymmetric induction by stereocentres of the alken- ylidene or double asymmetric induction by chiral selenenyl bromides on unsaturated imines with a chiral N-alkyl group resulted in diatereoselectivities up to 84:16. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) Scheme 1. General mechanism of the electrophile-induced cyclis- ation of unsaturated imines. the endo-trig mode, leading to ring 3 or 4, respectively. Fi- nally, cis-trans isomers can be formed when nucleophiles are added to the primary cyclisation products affording cyclic amine 6 or 7. A number of studies were devoted to the influence of different electrophiles and reaction conditions on the mode of the cyclisation of alcohols, [2–4,6] thio-