Abstract:Abstract-Photocycloaddition reactions which have been employed as one of the steps in the total/ synthesis of natural products are reviewed. The utility of the cycloadducts in these syntheses is also discussed.
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“…A few examples where photocycloadditions of various types have played an important role in synthesis are highlighted in Figures and . − 1 Representative molecules synthesized using various types of photocycloaddition as a key step. The kind of photocycloaddition involved is indicated in each case. 2 Representative molecules synthesized using [2 + 2] photocycloaddition as a key step.The photocycloaddition of the CC bond to various chromophores has been employed by synthetic chemists effectively. − To give a flavor of its usefulness an example from each type of cycloaddition is illustrated in Figure . These include meta-photocycloaddition, [5 + 2] photocycloaddition, [3 + 2] photocycloaddition, [6 + 2] photocycloaddition, [4 + 2] photocycloaddition, and [4 + 4] photocycloaddition .…”
Photochemistry, bearing significant applications in natural and man-made events such as photosynthesis, vision, photolithography, photodynamic therapy, etc., is yet to become a common tool during the synthesis of small molecules in a laboratory. Among other rationale, the inability to influence photochemical reactions with temperature, solvent, additives, etc., dissuades chemists from employing light-initiated reactions as a routine synthetic tool. This review highlights how diverse, highly organized structures such as solvent-free crystals and water-soluble host-guest assemblies can be employed to control and manipulate photoreactions and thereby serve as an efficient tool for chemists, including those interested in synthesis. The efficacy of the media in modifying the excited-state behavior of organic molecules is illustrated with photocycloaddition in general and [2 + 2] photocycloaddition in particular, reactions widely employed in the synthesis of complex natural products as well as highly constrained molecules, as exemplars. The reaction media, highly pertinent in the context of green sustainable chemistry, include solvent-free crystals and solids such as silica, clay, and zeolite and water-soluble hosts that can solubilize and preorganize hydrophobic reactants in water. Since no other reagent would be more sustainable than light and no other medium greener than water, we believe that the supramolecular photochemistry expounded here has a momentous role as a synthetic tool in the future.
“…A few examples where photocycloadditions of various types have played an important role in synthesis are highlighted in Figures and . − 1 Representative molecules synthesized using various types of photocycloaddition as a key step. The kind of photocycloaddition involved is indicated in each case. 2 Representative molecules synthesized using [2 + 2] photocycloaddition as a key step.The photocycloaddition of the CC bond to various chromophores has been employed by synthetic chemists effectively. − To give a flavor of its usefulness an example from each type of cycloaddition is illustrated in Figure . These include meta-photocycloaddition, [5 + 2] photocycloaddition, [3 + 2] photocycloaddition, [6 + 2] photocycloaddition, [4 + 2] photocycloaddition, and [4 + 4] photocycloaddition .…”
Photochemistry, bearing significant applications in natural and man-made events such as photosynthesis, vision, photolithography, photodynamic therapy, etc., is yet to become a common tool during the synthesis of small molecules in a laboratory. Among other rationale, the inability to influence photochemical reactions with temperature, solvent, additives, etc., dissuades chemists from employing light-initiated reactions as a routine synthetic tool. This review highlights how diverse, highly organized structures such as solvent-free crystals and water-soluble host-guest assemblies can be employed to control and manipulate photoreactions and thereby serve as an efficient tool for chemists, including those interested in synthesis. The efficacy of the media in modifying the excited-state behavior of organic molecules is illustrated with photocycloaddition in general and [2 + 2] photocycloaddition in particular, reactions widely employed in the synthesis of complex natural products as well as highly constrained molecules, as exemplars. The reaction media, highly pertinent in the context of green sustainable chemistry, include solvent-free crystals and solids such as silica, clay, and zeolite and water-soluble hosts that can solubilize and preorganize hydrophobic reactants in water. Since no other reagent would be more sustainable than light and no other medium greener than water, we believe that the supramolecular photochemistry expounded here has a momentous role as a synthetic tool in the future.
“…Photochemical cycloaddition between an alkene and an a,S-unsaturated ketone has proved to be a useful tool in synthesis (1)(2)(3)(4)(5). The process has been extensively employed for the preparation of cyclobutanes per se (2,3,(5)(6)(7)(8) and the method has also proved to be valuable for the generation of reactive four-membered rings that can undergo subsequent transformations (5.…”
Section: Introductionmentioning
confidence: 99%
“…The process has been extensively employed for the preparation of cyclobutanes per se (2,3,(5)(6)(7)(8) and the method has also proved to be valuable for the generation of reactive four-membered rings that can undergo subsequent transformations (5. 9).…”
The possible application in synthesis of a micellar solution as a medium in the photocycloaddition of enones to alkenes has been examined. It is found that the micelles are useful in increasing the effective concentration of reactants, have some ability in directing reaction regiochemistry, and may reduce hydrogen atom transfer in intermediate biradicals.
“…174 Image formation occurred on irradiating (>430 nm, 5-60 min) mixtures of monomer 121 and sensitizer 611 in a poly (methyl methacrylate) film.174 Monomer 121 was more sensitive and produced a clearer image than did the m-phenylene diester 58.174 The details of the crystal structure of the (S)-secbutyl ethyl diester 134 (a form) have been published,175 with the same conclusions noted previously. Irradiation times for photochemical polymerization, trimerization, and dimerization of 133 and 134 (Table VI) were [4][5][6] weeks (>300 nm, <5 °C).106'107…”
Section: Addendummentioning
confidence: 99%
“…179 The low enantiomeric excesses {<1%), of random chirality, were probably caused by microand macrotwinning involving enantiomeric domains and to technical difficulties associated with growth of such crystals from melts containing two components. 179 Additional experiments were reported on the asymmetric induction of crystallization by chiral additives, and the subsequent oligomerization of the monomers in these crystals by photocycloaddition (>300 nm, 5 °C, ~2 weeks). 177 The monomers 133 in the presence of 3-15% dimer (R)-132 or its enantiomer gave the same optically active oligomers, trimers, and dimers reported previously (Tables VI and VIII).…”
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