Lewis Acid Catalysis of Photochemical Reactions. 7. Photodimerization and Cross-Cycloaddition of Cinnamic Esters

Frederick D. Lewis*, Suzanne L. Quillen, Paul D. Hale, Joe D. Oxman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

112 Scopus citations

Abstract

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 SnCl4-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 π bonding and net charges. Solid-state photodimerization of free and complexed cinnamic esters and related molecules yield syn head-to-tail (α-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 methyl cinnamate—Lewis acid complex followed by reaction of the excited complex with 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.

Original languageEnglish (US)
Pages (from-to)1261-1267
Number of pages7
JournalJournal of the American Chemical Society
Volume110
Issue number4
DOIs
StatePublished - Feb 1 1988
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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