Aza-Morita−Baylis−Hillman Reactions and Cyclizations of Conjugated Dienes Activated by Sulfone, Ester, and Keto Groups

The aza-Morita−Baylis−Hillman reactions of aldimines 2 with several activated conjugated dienes were
found to proceed smoothly in DMF in the presence of 3-hydroxyquinuclidine (HQD). Imines 2 reacted
with 1-(p-toluenesulfonyl)-1,3-butadiene (3), methyl 2,4-pentadienoate (6), hexa-3,5-dien-2-one (7), and
1-phenylpenta-2,4-dien-1-one (8) to afford adducts 4, 13, 14, and 15, respectively. While products 4, 13,
and 15 were formed as E,Z mixtures, adducts 14 were obtained as essentially pure E-isomers. Cyclization
of the E-isomers of the products derived from the dienyl sulfone 3 and the dienoate ester 6 occurred via
intramolecular conjugate addition under base-catalyzed conditions to afford functionalized piperidines 5
and 16, respectively. The aza-Morita−Baylis−Hillman reaction and subsequent cyclization of the imine
2a with 3 were also carried out as a one-pot reaction, while the reaction mixture was simultaneously
irradiated at 300 nm to effect the photoisomerization of the unreactive Z-adduct of the corresponding 4
to the more reactive E-isomer.