Solid-state photocycloadditions

Chloranil, photocycloaddition with butadiene, 474 Chlorophylls, 552 Chu, N. Y. C 439 Ciamician, G., 1, 2,459 Cinnamic acid, solid state photodimerization, 476... 

Table 2. Reaction time, products, and yields of photocycloaddition reactions of inclusion complexes involving 11,17, and 21 in the solid state...

Powdered single crystals of 1 (ca. 20 mg) were sandwiched between two Pyrex cover glasses and placed in a polyethylene bag, which was irradiated with a 400-W high-pressure mercury lamp for 6 h (3 h for each side of the sample) in an ice-water bath. Out of seven carboxamides examined, la, le and lg showed intramolecular photocycloaddition in solid state to give the [4+4] cycloadducts 2a, 2e, and 2g in an almost quantitative yield after complete conversion, and If gave 2f in 9% yield. 

Steric Compression Inhibition of [2+2] Photocycloaddition. Following the pioneering work of Schmidt and co-workers on the solid state photodimerization reactions of the cinnamic acids... 

Kohmoto et al. examined the photocyclization of /V-cinnamoyl- l -naph-thamides (274a-f) in benzene solution and in the solid state [295] (Scheme 77). Intramolecular (2tt + 2tt) and (2tt + 4tt) photocycloaddition of styryl group to the naphthalene ring was observed in benzene solution, whereas 275a-c were also obtained in the solid state. 

The intramolecular [2 + 2] photocycloaddition of cyclohexadienone derivative 51, which is substituted with chiral piperidine ring in the solid state, proceeds enantioselectively and optically active products 52 and 53 were obtained [28], Two crystal modifications of 51, the a-form (mp 102-104°C) and (3-form (mp 127-128°C), gave optically active 52 and 53, respectively, upon irradiation in the solid state. 

A phase-selective photochemical reaction of 2-pyridones is observed. Irradiation of 225 in benzene gives mainly rearrangement products 226, whereas, in the solid state, [4+4] photocycloaddition to the photodimer 227 occurred in quantitative yield (Scheme 39) <20040L683>. The stereochemistry of the photodimer was exclusively the trans- /+configuration, as shown. This is presumably due to Jt-rt-stacking and dipole-dipole interactions between the pyridones. Intermolecular photocycloaddition of 2-pyridone mixtures can be selective and lead to useful quantities of [4+4] cycloaddition cross-products <1999JOC950>. 

Irradiation (313 nm) of films of polymers such as 1 leads to UV-Vis, IR, and solid-state 13C nmr changes attributed to a combination of 2 + 2 photocycloaddition and photo-Fries rearrangement [21], the latter presumably leading to cinna-moylphenol moieties, 2, in the irradiated polymer. Films irradiated at 313 nm in... 

Eycken and coworkers [121] employed ji-CDx as a chiral template for asymmetric induction in the intramolecular meta-photocycloaddition [126,127] of 4-phenoxy-1-butenes 48 and 50 in the solid state. (Scheme 19.)... 

Kohmoto et al. reported a fine example of absolute asymmetric synthesis involving the intramolecular [4 4- 4] photocycloaddition of 9-anthryl-Af-(naph-thylcarbonyl)carboxamide derivatives 42a-g in the solid state (Scheme 20) [26]. Out of seven carboxamides examined, 42a, 42e7 rid 42g showed intramolecular photocycloaddition in the solid state to give the [4 + 4] cycloadducts 43a, 43e, and 43g in almost quantitative yields after complete conversion and 42f gave 43f in 9% yield (Table 9). However, 42b, 42c, and 42d were unreactive. The crystals... 

Solid-state chiral photochemistry has been developed based on spontaneous chiral crystallization and supramolecular approaches. Since the report of solid-state [2 4- 2] photocycloaddition by Cohen and Schmidt in 1964 [11], the Weiz-mann Institute Group has been also a pioneer of solid-state chiral photochemistry. The research group first succeeded in absolute asymmetric [2 + 2] photocycloaddition by using chiral crystals spontaneously formed from achiral dienes in 1973 [12]. Thereafter, more than twenty successful examples of absolute asymmetric photoreactions have been reported by several research groups [9,10,13,14]. The... 

Dimethyl azodicarboxylate (164) has been reported to undergo a [ 4 + 2] photocycloaddition to the diene (165) to give the 2,3-diazabicyclo[2.2.2]octene (166). An analogous solid-state addition has been described in the ox-azolone (167) to give the photodimer (IbS), and oxidation of the photoadduct derived from 1-oxoanhydromethylberberine and nitrosobenzene has been used in a synthesis of ring C-substituted benzo[c]phenanthridines. ... 

As a suitable reaction we selected 2n + 2n) photocycloaddition as demonstrated by Schmidt, disubstituted ethylenes, appropriately oriented in the crystal and with the double bonds at a distance 4 A, form on u.v. irradiation cyclobutane dimers with a stereochemistry that directly reflects the symmetry relating the monomers in the mother phase (topochemical dimerization). Subsequently, Hasegawa and Naka-nishi have demonstrated that, when the double bonds are appropriately oriented and spaced, symmetrical disubstituted / -distyryl derivatives undergo, by the same mechanism, topochemical solid-state photopolymerization. 

Early studies of solid-state polymerization of vinyl derivatives have been reviewed (5). The initial discussions of the topochemicrd principle 0 were replete with examples from the photocycloaddition of cinnamic acid derivatives. 

Notably, in some cases photocycloaddition has been observed in the solid state in preference to other processes that are usually very fast. As an example, ketosulfone 36 did not undergo the expected photodecarbonylation reaction (see Section 2.2.1) but a very clean solid-to-solid intramolecular [2 + 2] cyclization to form the tetracyclic compound 37 as the only product in quantitative yield (Scheme 2.21). Small-scale reactions ca. 50 mg) could be completed also with sunlight within 2h and with no apparent changes in the aspect of the crystalline specimens. 

The photobiological activity of the psoralens is related, at least in part, to the ability of these coumarins to undergo [ 2 + 2] photocycloaddition to pyrimidine bases in DNA. The two cis-syn adducts (101) and (102) have now been obtained by irradiation of 2 -deoxycytidine in the presence of 3-carbethoxypsoralen, whereas reversible [ 2 + 2] dimerisation of the coumarin nucleus is preferred on solid state irradiation of the 8-alkoxypsoralen derivative (103). ° [ 2 +, 2] Photoadditions of 7-aminocoumarins... 

Following pioneering work on [2 + 2] cycloadditions of cinnamic acid in crystals,714 photocycloaddition in the solid state has become another systematically investigated reaction parameter. Crystallographic studies have shown that the distance... 

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