Photoisomerization 3-ionone

The 1,1-didesmethyl analogue (181) of abscisic acid (23) has been prepared.110 The cis-trans photoisomerization of (23) has been studied.111 A convenient procedure has been developed for the catalytic hydrogenation of p-ionone (142) to the m-5,6-dihydroionone (182).112 On treatment with Me2S+ CH, p-ionone gave the epoxide (183), which with MgBr2 afforded the aldehyde (184) without halohydrin formation.113... 

Other 2//-pyrans 81a were found to be photoisomerized to dienones 195 via valence-bond tautomers 80a by prolonged UV illumination (A. = 254 nm) (83CL651 83RTC302). The photochemical process started from excited singlet states, unlike the Z — E isomerization of j3-ionone-type precursors 79a, which proceeds via excited triplets (83RTC302). 

Singlet oxygen adds readily to tetrahydrobenzopyrans (166) derived from the photoisomerization of j6-ionone <73ABC224i> and its derivatives, for example (167) <88JMC713>, to afford the corresponding trioxanes (168) and (169) (Equation (21)). The saturated derivatives are obtainable by reduction with diimide in the case of (165) and (169 and by hydrogenation over Pt for (168). 

The photoisomerization of / -ionone (114) and / -ionylidene (115) derivatives in aqueous solution was inhibited in the presence of P-CD because of the restrictions imposed on the rotation of the double bond by the cavity. The only photoreaction observed was 1,5-H migration, which was probably promoted by a change in the nature of the lowest excited state from n,it to K,7t as induced by lowering the environment polarity [300]. 

The photoisomerization of retinal has been studied using super-short light pulses, and the neutral and protonated forms of the retinal analogue (47) have been examined by time-resolved methods.The irradiation of 3-ionone as a complex with P-CD in water leads only to the formation of retro-y-ionone." ... 

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