Lewis acid catalysis of photochemical reactions. 7. Photodimerization and cross-cycloaddition of cinnamic esters

Autor:	Paul D. Hale, Frederick D. Lewis, Suzanne L. Quillen, Joel D. Oxman
Rok vydání:	1988
Předmět:	chemistry.chemical_classification Methyl cinnamate Carboxylic acid General Chemistry Photochemistry Biochemistry Ethyl cinnamate Catalysis Cycloaddition Cinnamic acid Lewis acid catalysis chemistry.chemical_compound Colloid and Surface Chemistry chemistry Lewis acids and bases Enone
Zdroj:	Journal of the American Chemical Society. 110:1261-1267
ISSN:	1520-5126 0002-7863
DOI:	10.1021/ja00212a039
Popis:	The effects of Lewis acid complexation upon the molecular structure, solid-state photodimerization, and solution dimerization and cross-cycloaddition of cinnamic esters have been investigated. Comparison of crystal structures for free and SnCl/sub 4/-complexed ethyl cinnamate indicates that the enone double bonds are lengthened, the single bonds are shortened, and the enone conformation changes from s-cis to s-trans upon complexation. These changes are consistent with calculated changes in ..pi.. bonding and net charges. Solid-state photodimerization of free and complexed cinnamic esters and related molecules yield syn head-to-tail (..cap alpha..-truxillate) dimers. In most cases the Lewis acid complexes dimerize more efficiently and stereoselectively than the free esters. Photodimerization and cross-cycloaddition of methyl cinnamate in dilute solution is also catalyzed by Lewis acids. The mechanism of these reactions involves electronic excitation of a ground-state ester (dimerization) or simple olefin (cross cycloaddition). The catalytic effect of Lewis acids is attributed to an increase in excited-state lifetime and reactivity.
Databáze:	OpenAIRE
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