Abstract
Enamides 3a-c and 6 crystallize in α-packing modes with short intermolecular distances of 3.7–4.0 Å between alkene carbon atoms of adjacent molecules related by a center of symmetry. Irradiation at 350 nm of these crystalline tertiary phenylethenyl enamides affords head-to-tail dimers 8a-c and 9, respectively, in 87–92% yield, in marked contrast to the E to Z isomerization that is the exclusive reaction upon solution irradiation of enamides 3a and 6.