SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF THE DOUBLY LOCKED 9E,11Z RETINAL MODEL SYSTEMS 7E,13E-11,19-10,20-DIMETHANORETINAL AND ITS 13Z ISOMER

7E,13E-11,19-10,20-dimethanoretinal (1) and its 13Z isomer 2 were prep ared from beta-ionone, using the novel synthon 2-(diethoxyphosphinyl)- 5,5-dimethoxyhexanenitrile. This synthon was also used to prepare 7E,9 E,13E-10,20-methanoretinal (3) and its 13Z isomer 4 in high yield, sta rting from beta-ionone. Spectroscopic analysis (mass, H-1 and C-13 NMR and UV/Vis) of these compounds is discussed. The introduction of the methano bridges leads to minimal steric and electronic changes. The ph otostationary state reached from 1 and 2 has the 13Z form 2 as the mai n constituent. This is one of the very few with a Z form as the main c onstituent of the photostationary state. 1 and 2 are very sensitive to acid-catalyzed isomerization of the 13-C = 14-C double bond. The pres ence of the 11,19-methano bridge is responsible for this efficient Z-E isomerization.