We would like to disclose an efficient synthesis of 2-unsubstituted, 2-alkyl and 2-aryl substituted 3-pyrrolines via a phosphine catalyzed (4+1) reaction of readily accessible allenylic carbamates.  The introduction of a carbamate moiety on the �'-carbon of the allenoate lead to an unprecedented rearrangement to 3-pyrrolines via in situ formation of a sulfonamide anion and a phosphonium diene upon attack by phosphine.  Evidence has been obtained that suggests the reaction proceeds via initial addition of the nucleophile to the �'-carbon of the phosphonium diene followed by an intramolecular ?-umpolung addition to form the 3-pyrroline. Thirteen examples will be described where the yield ranges from 28-74%. The electronic effects of the nucleophile were explored by varying the substituent on the arene ring of the sulfonamide.  The newly developed methodolgy was then applied toward the formal syntheses of the pyrrolizidine natural products (�)-trachelanthamidine and (�)-supinidine.

Phosphine catalyzed (4+1) reaction: Rearrangement of allenylic carbamates to 3-pyrrolines

244th National Meeting (2012)

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