High Pressure Promoted 4+2/3+2 Tandem Cycloadditions of Nitrostyrene and Enol Ethers

摘要

Tandem [4+2]/[3+2] cycloadditions of nitroalkenes with electron-rich and electron-poor alkenes have been applied by Denmark et al. in the synthesis of several natural pyrrolizidine alkaloids as (-) hastanecine, (-) rosmarinecine and (-) crotanecine~1,2. In these tandem cycloadditions an electron-rich alkene reacts with a nitroalkene in an inverse electron demand Diels-Alder reaction under formation of a nitronate (mono-adduct), which then reacts with a second alkene in a [3+2] cycloaddition, leading to a nitroso acetal (di-adduct)