Stereoselective Synthesis of Pyrrolizidine Alkaloids from Nitroalkanones

Article abstract of DOI:10.1002/hlca.19910740624

Reduction of 5-nitropentadecane-2,8-dione (11), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec-1-en-3-one, gave, depending on the conditions, two epimeric 3-heptyl-2,3,5,6,7,7a-hexahydro-5-methyl-1H-pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα-hydro epimer 1b with cis-oriented H-atoms at C(3), C(5), and C(7a).NaBH3CN/NH4OAc reduction of the nitro-dione 11 yielded all four diastereoisomers with the 7aβ-hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp.The N-atom of the pyrrolizidine ring stems from NH4OAc exclusively as shown by reduction of 11 with NaBH3CN/(¹⁵N)H4OAc.