A New Synthetic Approach to (+)‐Hyacinthacine A 1 and the First Total Synthesis and Absolute Configuration Assignment of Naturally Occurring (+)‐Hyacinthacine A 6

Naturally occurring (1 S ,2 R ,3 R ,7a R )‐1,2‐dihydroxy‐3‐hydroxymethylpyrrolizidine [(+)‐hyacinthacine A 1 ( 1 )] and(1 S ,2 R ,3 R ,5 R ,7a R )‐1,2‐dihydroxy‐3‐hydroxymethyl‐5‐methylpyrrolizidine [(+)‐hyacinthacine A 6 ( 2 )] have been synthesized by Wittig's methodology using aldehyde 7 , prepared from (2 R ,3 S ,4 R ,5 R )‐3,4‐bis(benzyloxy)‐2′‐ O ‐( tert‐ butyldiphenylsilyl)‐2,5‐bis(hydroxymethyl)pyrrolidine ( 3 , partially protected DALDP), as the homochiral starting material and the appropriated ylide to afford either the corresponding α,β‐unsaturated ester 8 or ketone 9 , which were submitted to internal lactamization and reductive amination, respectively, to give the corresponding intermediate pyrrolizidin‐5‐one 11 and the totally protected pyrrolizidine 14 . Compounds 11 and 14 were easily transformed into the above hyacinthacines 1 and 2 , respectively.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)