Photocycloaddition reactions solid state

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

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... 

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>. 

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. 

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. 

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... 

Nieuwendaal et al. have detected a phase transition during the progress of the solid-state [2 + 2] photocycloaddition reaction of a-trans-chmaxnic acid. The reaction was monitored using CPMAS experiments as a function of irradiation time. Two different crystal polymorphs of a-truxillic acid were observed. 

Abstract. The asymmetric synthesis of chiral polymers by topochemically controlled polymerization in chiral crystals is discussed. Following a short survey of topochemical polymerization in the solid state and some comments on chiral crystals, we present the requirements for the performance of asymmetric polymerization based on [2+2]-photocycloaddition. The planning and execution of two successful polymerizations of this sort are described. In the first, we start with a chiral non-racemic monomer and obtain optically active cyclobutane oligomers. The optical yields of the dimer and trimer were quantitative on the scale of N.M.R. sensitivity. In the second reaction we start with a racemate, and by the processes of crystallization in a chiral structure and solid-state reaction we generate an optically active polymer, in the absence of any outside chiral agent. The possible application of this novel method to additional systems is discussed. 

A systematic study was performed in this laboratory, under the leadership of the late G. M. J. Schmidt, on solid-state (2+2)-photocycloadditions [10]. The /rans-cinnamic acids provide a clear example of the structural requirements of these reactions [16, 17]. We dis-... 

In many respects, the present results resemble the pioneering work of the late G. M. J. Schmidt and his co-workers at the Weizmann Institute of Science, who used crystal structure-solid-state reactivity correlations to elucidate the geometric requirements for intermolecular [2+2]-photocycloaddition. In both his case and ours, distance and angular requirements for reaction were established and the structure and stereochemistry of the products were shown to be simply and directly related to the molecular structure existing in the bulk crystal. 

Photocycloaddition is one of the best known reactions in solid-state organic photochemistry. The reactions, in general, occur more selectively and efficiently than in homogeneous solution due to tight and regular molecular arrangements in crystals. It is often observed that the photoproducts in the solid state are entirely different from those in solution. 

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