Reaction of the 5‐Azoniafulvene Ion with Enamines: A New Approach to Pyrrolizines

Abstract

The synthesis of N,N-dimethyl-N-[(pyrrol-l-yl)methyl]anilinium chloride (14) and of the corresponding p-toluidinium salt 15 is described. These salts, when dissolved in polar solvents, are shown to be in equilibrium with 1-(chloromethy1)pyrrole (17) and thereby potentially with the 5-azoniafulvene ion (2). Consequently, they react under very mild conditions (MeCN, 60') with enamines to give pyrrolizine derivatives in acceptable yield (40-50%). The process is rationalized in terms of an initial Mannich-type reaction which is immediately followed by a cyclization.

Enantioselective Synthesis of α‐Aryl‐β2‐Amino‐Esters by Cooperative Isothiourea and Brønsted Acid Catalysis

“…N,N-Dibenzyliminium ion 45 was prepared from hemiaminal ether 5 using TMSCl (trimethylsilyl chloride) [35] and used as as toichiometric electrophile in ar eaction with (R)-BTM and ester 8 in the presence of Bn 2 NEt. b-Amino ester 9 was generated in 65 %y ield and 92:8 er,c onsistent with iminium ion 45 being ap otential intermediate in this reaction process.G iven the known ability of tertiary amines to add reversibly to iminium ions, [36] further consideration led to the possibility of the iminium ion 45 being intercepted in situ by the Lewis base (R)-BTM. Addition of (R)-BTM to N,N-dibenzyliminium chloride 45 showed complex behavior and gave am ixture of products by 1 HNMR analysis,w ith aminomethylation of the Lewis base to give 46 tentatively assigned as asignificant component.…”