Diastereoselective Cyclisation of N‐Alkenylideneamines into 3,4‐Dihydro‐2H‐pyrrol‐1‐ium Halides

Abstract

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-(alkenylidene)alkylamines and subsequent reduction. These cyclisations 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-

Recent Advances in Organoselenium Chemistry

“…A number of 2‐(α‐selenoalkyl)pyrrolidines were synthesized by a similar selenocyclization. Asymmetric induction by stereocentres in the substrate or double asymmetric induction by additional chiral selenenyl bromides resulted in diastereoselectivities up to 84:16 85. 2,4,6‐Triisopropylphenylselenenyl bromide has been reported by Lipshutz to give improved selectivities in electrophile‐mediated cyclizations of homoallylic alcohols to tetrahydrofurans as compared to phenylselenyl chloride 86.…”

“…Asymmetric induction by stereocentres in the substrate or double asymmetric induction by additional chiral selenenyl bromides resulted in diastereoselectivities up to 84:16. [85] 2,4,6-Triisopropylphenylselenenyl bromide has been reported by Lipshutz to give improved selectivities in electrophile-mediated cyclizations of homoallylic alcohols to tetrahydrofurans as compared to phenylselenyl chloride. [86] The use of this reagent gave the best results when applied to the cyclization of 36, leading to selenide 37 in 74 % yield with a diastereomeric ratio of 88:12 (Scheme 28).…”

Tandem intramolecular cyclisation/1,3-aryl shift in N-(4,4-diethoxybutyl)-1-arylmethanimines (Kazan reaction): synthesis of 3-benzylidene-1-pyrrolines

“…11,12 Examples of such intramolecular reactions, which give rise to pyrrolidine ring, is the acid-mediated cyclization of N-(1-phosphoryl-4-chlorobutyl)imines 13 and cyclization of g,d-alkenylimines under the action of electrophilic reagents. [14][15][16][17] An approach to the synthesis of proline derivatives from ketals and acetals of 2-((diphenylmethylene)amino)-5oxopentanoic and 2-((diphenylmethylene)amino)-5-oxohexanoic acids under the action of triuoroacetic acid described in the recent work should particularly be mentioned. 18 However, very few of these methods allow for simultaneous intramolecular C-N bond formation and intermolecular formation of a carbon-carbon bond.…”

Highly Stereoselective Synthesis of β‐Lactams Utilizing α‐Chloroimines as New and Powerful Chiral Inductors

“…In this way, 13 was obtained after 2 h at À30 8C in acetone (Scheme 6). To evaluate the chiral purity of aldehyde 13, condensation with (R)-a-methylbenzylA C H T U N G T R E N N U N G amine [17] was performed by means of standard reaction conditions in dichloromethane towards the corresponding imine 19 (Scheme 6). The latter imine was obtained in a diastereomeric excess of 92 % (based on 1 H NMR and GC), which corresponds well with the ee values reported for the enantioselective chlorination of other aldehydes using the same methodology (91-95 %).…”