An asymmetric [3+2] annulation reaction to form 3-pyrroline products is reported. Upon treatment with lithium diisopropylamide, readily available ethyl 4-bromocrotonate is deprotonated and trapped with Ellman imines selectively at the α-position to yield enantiopure 3-pyrroline products. This new method is compatible with aryl, alkyl, and vinyl imines. The efficacy of the method is showcased by short asymmetric total syntheses of (-)-supinidine, (-)-isoretronecanol, and (+)-elacomine. This novel annulation approach also works for an aldehyde, thus providing access to a 2,5-dihydrofuran product in a single step from simple precursors. By modifying the structure of the carbanion nucleophile, an asymmetric vinylogous aza-Darzens reaction can be realized.
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