2-(Acyloxy)vinyl ethers undergo regioselective [4 + 2] cycloadditions with nitroalkenes (promoted by SnCl4) to afford substituted 5-acetoxy nitronates in good yields (68–91%). Endo/exo selectivity in the cycloadditions has been found to be dependent on the nitroalkene substitution; 2-aryl-1-nitroalkenes provided exclusively exo cycloadducts while 2-cyclohexyl-1-nitroalkene 28 afforded predominately endo cycloadducts in a ratio of 12:1. The resulting nitronates can be elaborated to N-tosyl-4-substituted-3-hydroxypyrrolidines by hydrogenolysis (160 psi of H2/PtO2) or to bicyclic α-hydroxy lactams by [3 + 2] cycloaddition followed by hydrogenation (14.7 psi of H2/Raney nickel). A chiral 2-acetoxyvinyl ether derived from (R)-2,2-diphenylcyclopentanol has been employed in the cycloaddition‒hydrogenation sequence to prepare an optically active N-tosyl-3-hydroxypyrrolidine in 96% ee.
ASJC Scopus subject areas
- Organic Chemistry