Diastereoselectivity in Photochemistry
Abstract
Diastereoselective photochemical reactions play an important role for asymmetric synthesis, for example for the synthesis of natural or biologically active compounds. Chirality is either induced by a chiral auxiliary or by a chiral centers already present in the substrates. In the first case, the source of chirality is removed during the ongoing multistep synthesis. In the second case, the chirality source is conserved in the target compound. In the present chapter examples of the [2+2] photocycloaddition of carbonyl compounds with alkenes (Paternò-Büchi reaction), between α,β-unsaturated carbonyl compounds and alkenes as well as between two alkenes are discussed. Typical diastereoselective photocycloaddition reaction with aromatic compounds are reported. Currently, photoinduced radical reactions are intensively investigated and photoredox or more generally photocatalysis play a key role. In such reactions neutral radicals and radical ions are typical intermediates. Under photochemical conditions, tautomeric equilibria significantly change. Due to this fact, interesting diastereoselective reactions have been reported. Electrocyclization has often been applied to the synthesis of heterocyclic compounds. Photochemical rearrangements provide convenient accesses to complex polycyclic compounds. The diastereoselectivity is significantly increased when the corresponding reactions are carried out under confinement conditions, for example with inclusion complexes. Photooxygenation with singlet oxygen is a very convenient oxidation method. Generally, such reactions are highly regio stereo and chemoselective.
Keywords
Chiral auxiliary Chiral induction Diastereoselectivity Double induction Electrocyclization Electronic excitation Hydrogen atom transfer Inclusion complexes Natural products Photochemical sensitization Photochemistry Photocycloadditions Photooxygenation Photo-tautomerization Radical reactions
Chiral auxiliary
Chiral induction
Diastereoselectivity
Double induction
Electrocyclization
Electronic excitation
Hydrogen atom transfer
Inclusion complexes
Natural products
Photochemical sensitization
Photochemistry
Photocycloadditions
Photooxygenation
Photo-tautomerization
Radical reactions
Domains
Chemical Sciences
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