Synthesis of (±)-Crispine A via a Nitrosoalkene Hetero-Diels-Alder Addition to Ethyl Vinyl Ether

The synthesis of (±)-crispine A in 9 steps and 24% overall­ yield was achieved using a nitrosoalkene hetero-Diels-Alder­ addition to ethyl vinyl ether as the key step. The synthesis starts from commercial 3,4-dimethoxyphenylacetic acid and uses simple methods, easily accessible materials and inexpensive reagents. An isochroman derivative was unexpectedly formed in an attempted reduction of a dihydro-4H-1,2-oxazine intermediate.