HIGH-EFFICIENCY MICROPHOTOOXIDATION OF 2,3,4,5-TETRAPHENYLFURAN USING MILLIWATT LED SOURCES
Kang, Ye Chan
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We studied the photooxidation of 2,3,4,5-tetraphenylfuran using O2 under pressure to make 1,2,3,4-tetraphenyl-2-buten-1,4-dione, of interest in natural product synthesis. We used methylene blue as energy sensitizer and a LED source to excite O2 for reaction at room temperature. This new methodology is not only inexpensive and green, but also leads to diverse access of natural product motifs. Methylene blue is known to absorb 600 – 700 nm light. As we increased the wavelength of the LED source, the percent conversion of 2,3,4,5- tetraphenylfuran to 1,2,3,4-tetraphenyl-2-buten-1,4-dione increased. The Z (cis) diastereomer was observed to dominate over the E (trans) diastereomer. The percent conversion from starting compound to product was highest using a 627 nm LED source. The highest ratios of Z to E products were also observed at this wavelength. We also verified that photoisomerization of the 1,2,3,4–tetraphenyl-2-buten-1,4-dione does not occur under the conditions of the photooxidation.