Cohen; Scott; Neukom; et al.
Helvetica Chimica Acta, 1981 , vol. 64, # 4 p. 1158 - 1173

Coffen, David L.; Cohen, Noal; Pico, Anthony M.; Schmid, Rudolph; Sebastian, Mark J.; Wong, Frederick
Heterocycles, 1994 , vol. 39, # 2 p. 527 - 552