P-Truxinates

Diquercetin 3-galactoside ester of tetrahydroxy-p.-truxinic acid (monochaetin, 13.6) Monochaetum multiflorum leaves Melastomataceae 360... 

FIGURE 5. Presumed geometry of the trans-stilbene chiral fumarate exciplex precursor of the p-truxinate cycloadduct. 

Scheme 3 Photodimerisation of trans-cinnamic acid (9) and three of the possible diastereomers, the a-truxillic acid (10), the p-truxinic acid (11) and the 5-truxinic acid (12)...

After 2 days P-monomer after 6 days mainly 2,2 -diethoxy-P-truxinic acid... 

Dichloro-substituted, methylenedioxy-substituted, or sulfur-containing planar aromatic molecules often crystallize in 3 structures. These effects were utilized to design [2-1-2] photoreactive molecular complexes [30]. Cocrystallization from EtOH of 6-chloro-3,4-methylenedioxycinnamic acid with 2,4-dichlorocin-namic acid and with 3,4-dichlorocinnamic acid (all three cinnamic acids are 13-type [2-1-2] photoreactive crystals) gave the 2 1 and 1 1 complexes, respectively. Irradiation of these complexes yielded mixtures of three P-truxinic dimers in a statistical ratio (Scheme 9). This result, together with the crystal structures of the component acids, indicates that each sheet that is stabilized by an interstack... 

The photostability was ascribed to the presence of the low-lying CT state. The complexes 19a-19e and 19a-19f were also photostable. On the other hand, the 1 1 molecular complex of 3,5-dinitrocinnamic acid with 2,5-dimeth-oxycinnamic acid 19b- 19c (the double bond center-to-center separation 3.54 A) as well as 19b- 19d and 19b- 19e were photoreactive, producing the corresponding unsymmetric p-truxinic dimers in 60% yields. 

Although earlier claimed to be unsuccessful, the photochemical reaction of stilbene with fumaric ester has now been used to synthesize p-truxinic acid (212). 

The photodimerisation of cinnamic acid can be controlled by irradiation of its double salts with certain diamines in the solid state. Thus, the double salt crystal of cinnamic acid and o-diaminocyclohexane gave upon irradiation in the solid state, P-truxinic acid as the major product (Scheme 129)P ... 

Hydroxycinnamic acids are present in plants, where they play an important role in controlling the structure of cell walls. It should come as no surprise, therefore, that cyclodimerization products of naturally occurring cinnamate and coumarin derivatives, such as p-coumaric acid and ferruHc acid, have been isolated from a variety of plants. It has been postulated that dimers are formed by a photoinduced mechanism, causing cross-linking of the polysaccharide chains. For example, sagerinic acid isolated from sage Salvia officinalis) was identified as the uncommon p-truxinate dimer 2, presumably the result of the [2 + 2]-cyclodimerization of rosmarinic acid 1 present in the plant. ... 

Connection of two cinnamate chromophores has frequently been used to attain high local concentrations of reactants, thereby circumventing the inefficiency of the above-mentioned bimolecular dimerization reactions. An extreme example of this approach is embodied in the cyclophane structures 3, in which two cinnamate moieties undergo photodimerization to give quantitatively the P-truxinate dimer with a quantum yield of Similarly, the bis-cinnamamide 4 furnished 48% of P-truxinimide upon... 

Coates et al. used stacking interactions in the phenyl-perfluorophenyl system to direct co-crystal-lization of mixed stilbene and cinnamic acid co-crystals, thereby directing the formation of the mixed P-truxinic acid derivative in very high yield. Ito has recently reviewed the solid-state organic photochemistry of mixed crystals. " ... 

Photodimerization of trans-cinnamic add 47 is controlled by the formation of a double salt with diamines.It is known that 47 gives a-truxUlic add 49 efiidently on irradiation. The double salt crystals of 47 and ds-1,2-cydohexanediamine 48, on the other hand, yield P-truxinic acid 50 predominantly. 

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