Se. Denmark et A. Thorarensen, THE TANDEM CYCLOADDITION CHEMISTRY OF NITROALKENES - A NOVEL SYNTHESIS OF (-)-HASTANECINE, Journal of organic chemistry, 59(19), 1994, pp. 5672-5680
A short and efficient asymmetric synthesis of the pyrrolizidine necine
base (-)-hastanecine is described. The key reaction in the synthesis
is a sequential inter [4+2]/inter[3+2] cycloaddition. The Lewis acid p
romoted [4+2] cycloaddition between 2-acyloxy nitroalkene 16 and chira
l vinyl ether 17 afforded a nitronate which underwent facile [3+2] cyc
loaddition with dimethyl maleate. The resulting nitroso acetal 19 had
all the required stereocenters for (-)-hastanecine. The critical unmas
king of the nitroso acetal 19 employed a hydrogenolytic cleavage to gi
ve the 1-azabicyclo-[3.3.0]octane skeleton of (-)-hastanecine.