| Popis: |
The major applications of organic photochemical processes to synthetic problems have to date focused for the most part on the use of photocycloadditions and electrocyclizations in the preparation of strained ring compounds in target systems or key synthetic intermediates. The utility of these methods in selected preparative sequences for construction of natural and/or theoretically interesting products has been reviewed.(1) In general, these excited-state reactions share several unique features which make their utility in synthetic chemistry particularly advantageous. For example, photocycloadditions serve as useful methods for generating carbon-carbon bonds in strained ring systems which, due to their high energy content, are capable of participating in facile ring cleavage processes leading to desired intermediates. Similarly, electrocyclizations lead to the installation of difficultly prepared cyclic units from more readily available acyclic precursors. The applications of these reactions to synthetic problems is further broadened by their predictable regiochemical and stereochemical courses utilizing simple molecular orbital methods. Other classes of excited-state reactions have been used for the introduction and interconversion of functionality in molecular systems. Thus, several classes of photochemical processes appear compatible with the criteria established for evaluation of synthetically useful gound-state transformations. |
