Flora Chow

Bio: Flora Chow is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Reductive elimination & Solvent effects. The author has an hindex of 6, co-authored 6 publications receiving 429 citations.

Selenium stabilized carbanions. .alpha.-Lithio selenoxides as reagents for the synthesis of olefins, allyl alcohols, and dienes

Abstract: Techniques for the preparation of a-lithio selenoxides have been developed. These reagents react cleanly with most aldehydes and ketones to give 0-hydroxy selenoxides, which can be thermolyzed to allyl alcohols or reduced to hI result of the limited acidifying power of the phenylseleno group, and the propensity of selenides to be fragmented upon treatment with powerful metalating agents. The substantially greater acidity expected for selenoxides, however, should allow their deprotonation in cases where the corresponding selenides are insufficiently acidic. The greater acidity of selenoxide vs. selenide can be inferred from comparisons with kinetic and thermodynamic acidity data available for sulfides, sulfoxides, and sulfones. Bordwell and co-workers5 have reported the following pK, data (Me2SO solvent and references).

Selenium stablized anions. Conversion of β-hydroxy selenides into olefins

Abstract: Sulphonylation of β-hydroxy selenides, prepared by addition of organometallic compounds to carbonyl compounds, results in reductive elimination to give olefin under unusally mild conditions.

Why Nature Chose Selenium

Abstract: The authors were asked by the Editors of ACS Chemical Biology to write an article titled “Why Nature Chose Selenium” for the occasion of the upcoming bicentennial of the discovery of selenium by the Swedish chemist Jons Jacob Berzelius in 1817 and styled after the famous work of Frank Westheimer on the biological chemistry of phosphate [Westheimer, F. H. (1987) Why Nature Chose Phosphates, Science 235, 1173–1178]. This work gives a history of the important discoveries of the biological processes that selenium participates in, and a point-by-point comparison of the chemistry of selenium with the atom it replaces in biology, sulfur. This analysis shows that redox chemistry is the largest chemical difference between the two chalcogens. This difference is very large for both one-electron and two-electron redox reactions. Much of this difference is due to the inability of selenium to form π bonds of all types. The outer valence electrons of selenium are also more loosely held than those of sulfur. As a result,...

Metal-Catalyzed 1,2-Shift of Diverse Migrating Groups in Allenyl Systems as a New Paradigm toward Densely Functionalized Heterocycles

Abstract: A general, mild, and efficient 1,2-migration/cycloisomerization methodology toward multisubstituted 3-thio-, seleno-, halo-, aryl-, and alkyl-furans and pyrroles, as well as fused heterocycles, valuable building blocks for synthetic chemistry, has been developed. Moreover, regiodivergent conditions have been identified for C-4 bromo- and thio-substituted allenones and alkynones for the assembly of regioisomeric 2-hetero substituted furans selectively. It was demonstrated that, depending on reaction conditions, ambident substrates can be selectively transformed into furan products, as well as undergo selective 6-exo-dig or Nazarov cyclizations. Our mechanistic investigations have revealed that the transformation proceeds via allenylcarbonyl or allenylimine intermediates followed by 1,2-group migration to the allenyl sp carbon during cycloisomerization. It was found that 1,2-migration of chalcogens and halogens predominantly proceeds via formation of irenium intermediates. Analogous intermediate can also be...